<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:7bbed507-8673-4b66-ab45-07e4915e856b,g:0785a775-d7f9-4ff1-bae1-b6a1e9f0ea94-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="upst-20220630.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="i0a466b9cda3f4ee486fbc070f9c53e45_CondensedConsolidatedBalanceSheetsParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsFairValueDisclosure_af5b9d04-4f28-44ee-934d-d43509c3704b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_OtherAssetsFairValueDisclosure_af5b9d04-4f28-44ee-934d-d43509c3704b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure_83e7b999-33c1-474b-b2d3-37cbb8f194e3" xlink:href="upst-20220630.xsd#upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure_83e7b999-33c1-474b-b2d3-37cbb8f194e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_1cd78943-f301-49ab-a9e8-a3cf112986a7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_1cd78943-f301-49ab-a9e8-a3cf112986a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_353c9a81-e55d-479c-9aea-f09a004316d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_353c9a81-e55d-479c-9aea-f09a004316d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_e28ca42f-f054-4e24-9abb-70c64ee9a1b4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_CommonStockSharesIssued_e28ca42f-f054-4e24-9abb-70c64ee9a1b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_1077ae5c-5165-4b7b-9590-2bdde897228a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_1077ae5c-5165-4b7b-9590-2bdde897228a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_558cb7b7-46cd-4201-aede-5b017eec432b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_558cb7b7-46cd-4201-aede-5b017eec432b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_558cb7b7-46cd-4201-aede-5b017eec432b" xlink:to="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_f29baa8c-9cbd-45eb-ad2d-9665022e8fb8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:to="loc_us-gaap_Cash_f29baa8c-9cbd-45eb-ad2d-9665022e8fb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_e979726e-98e9-4659-a792-4caeeba3d97e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:to="loc_us-gaap_RestrictedCash_e979726e-98e9-4659-a792-4caeeba3d97e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_c1253615-e9f8-4664-9776-3e8d85489d81" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:to="loc_us-gaap_NotesReceivableNet_c1253615-e9f8-4664-9776-3e8d85489d81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_2bf40761-df0d-464b-872a-d9526c161402" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:to="loc_us-gaap_OtherAssets_2bf40761-df0d-464b-872a-d9526c161402" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_342c2ed9-10cb-4df9-982d-03b5cafb20e7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_e47fa916-78ed-49b3-bb0b-82dbb042062f" xlink:to="loc_us-gaap_Assets_342c2ed9-10cb-4df9-982d-03b5cafb20e7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsFairValueDisclosure_be07f25f-ec12-4ce5-b31d-5aa17fc0858a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsFairValueDisclosure"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_558cb7b7-46cd-4201-aede-5b017eec432b" xlink:to="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_80d235a1-f141-46c1-ab9b-e5b910681a61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_80d235a1-f141-46c1-ab9b-e5b910681a61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_b5adb32f-6834-44c3-baf6-fbe386916322" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_b5adb32f-6834-44c3-baf6-fbe386916322" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_0a864542-a425-465a-8365-ad6ea211e5ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:to="loc_us-gaap_Liabilities_0a864542-a425-465a-8365-ad6ea211e5ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_ab7e8250-34dd-47a8-9191-1f343d48b1eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_9154da46-bec8-41de-a804-18a371ac3cab" xlink:to="loc_us-gaap_StockholdersEquity_ab7e8250-34dd-47a8-9191-1f343d48b1eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_606a3020-31fa-445e-b7b2-230d31f231f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c537e343-8b59-4ea0-ab77-f22632aab0a5" xlink:to="loc_us-gaap_StatementTable_606a3020-31fa-445e-b7b2-230d31f231f8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_606a3020-31fa-445e-b7b2-230d31f231f8" xlink:to="loc_srt_ConsolidatedEntitiesAxis_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_247cde54-3c6e-4032-9b2b-e655977d9362" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_6568b6ba-ab76-47f6-8bc0-7bacfbc413e4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_247cde54-3c6e-4032-9b2b-e655977d9362" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_a93aa542-1265-4abf-bda3-2ea45c09108c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_247cde54-3c6e-4032-9b2b-e655977d9362" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_a93aa542-1265-4abf-bda3-2ea45c09108c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="upst-20220630.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended" id="i292fdfca84814d68a94097b9f5f5fa7c_CondensedConsolidatedStatementsofStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_745b3d62-08b2-4759-8d2d-939bcb08671c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_745b3d62-08b2-4759-8d2d-939bcb08671c" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_de63db99-b7c0-4f91-8956-9c9014b59eba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_de63db99-b7c0-4f91-8956-9c9014b59eba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_e67870de-2cda-48fa-a0f6-977200a15abe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockholdersEquity_e67870de-2cda-48fa-a0f6-977200a15abe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_bf6461dd-161a-4212-86d0-a79e6e681775" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_bf6461dd-161a-4212-86d0-a79e6e681775" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_36a06c38-40be-4d70-885d-95dce561a4c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_36a06c38-40be-4d70-885d-95dce561a4c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_e0025db8-1564-451c-bdcd-3f4e2d56f6b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_e0025db8-1564-451c-bdcd-3f4e2d56f6b5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ExerciseOfCommonStockWarrantsShares_ac257090-f4a6-4de2-b72c-d89908c21896" xlink:href="upst-20220630.xsd#upst_ExerciseOfCommonStockWarrantsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_upst_ExerciseOfCommonStockWarrantsShares_ac257090-f4a6-4de2-b72c-d89908c21896" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition_59e4e583-ddd9-45cc-ab78-848985bbcc32" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition_59e4e583-ddd9-45cc-ab78-848985bbcc32" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e8cad427-d875-4618-9ad2-2b41757c2c6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e8cad427-d875-4618-9ad2-2b41757c2c6e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_c8cea2e0-e25e-4f0f-8ed8-1b3061a11b19" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_c8cea2e0-e25e-4f0f-8ed8-1b3061a11b19" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_414d334b-3cd6-4a06-9d9c-cbaa090503f1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_414d334b-3cd6-4a06-9d9c-cbaa090503f1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_06d84e4e-d9e9-4e90-81aa-9f7816863205" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_06d84e4e-d9e9-4e90-81aa-9f7816863205" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ad722528-0314-408b-beb1-9cde24252f57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ad722528-0314-408b-beb1-9cde24252f57" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_054b2a10-68b4-4a1c-b10c-58de4759103c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_054b2a10-68b4-4a1c-b10c-58de4759103c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_0c93092d-c1df-41b1-bdc7-4dd2cce3db75" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_0c93092d-c1df-41b1-bdc7-4dd2cce3db75" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_d412b2fb-5982-4633-941b-27f56d136c17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_d412b2fb-5982-4633-941b-27f56d136c17" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_286c9d18-9c2a-4cde-94dd-cb3f38db0953" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_286c9d18-9c2a-4cde-94dd-cb3f38db0953" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_37f22697-d92c-458b-9873-9119da922bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_37f22697-d92c-458b-9873-9119da922bb4" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_9a82f3f3-9d1f-4587-bf7c-52881b92ebb0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_765e5503-b497-4c74-84ad-5bd2d1f5c418" xlink:to="loc_us-gaap_NetIncomeLoss_9a82f3f3-9d1f-4587-bf7c-52881b92ebb0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_aded055c-e0e1-49e2-a36e-b6783736b52e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_80e70600-8a5f-4274-aa27-e24a6cdf4cca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8f3f01e9-3949-466c-a9b5-18fcd4f4eefd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_745b3d62-08b2-4759-8d2d-939bcb08671c" xlink:to="loc_us-gaap_StatementTable_8f3f01e9-3949-466c-a9b5-18fcd4f4eefd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8f3f01e9-3949-466c-a9b5-18fcd4f4eefd" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a" xlink:to="loc_us-gaap_EquityComponentDomain_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_66174798-674d-444e-a7b9-86c375d9ed91" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c115054c-9f6c-408e-9a59-e6a4dcf0ed9a" xlink:to="loc_us-gaap_EquityComponentDomain_66174798-674d-444e-a7b9-86c375d9ed91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_d4604951-6b11-43bd-b2fc-094a0fa27ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_66174798-674d-444e-a7b9-86c375d9ed91" xlink:to="loc_us-gaap_CommonStockMember_d4604951-6b11-43bd-b2fc-094a0fa27ae6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_59243619-7f08-4aa6-8c80-3cef1e9522c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_66174798-674d-444e-a7b9-86c375d9ed91" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_59243619-7f08-4aa6-8c80-3cef1e9522c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_88437a42-2efc-4592-99cd-faf60e4d282b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_66174798-674d-444e-a7b9-86c375d9ed91" xlink:to="loc_us-gaap_RetainedEarningsMember_88437a42-2efc-4592-99cd-faf60e4d282b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#RevenueDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="extended" id="i6293bd4a323f4d2e8aa9177e74e755d6_RevenueDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_93a113b8-6e2a-49ca-a3ee-1b81afdf8834" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_0d996fe4-1adb-47f4-8cf2-7a7e85e45ec4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_93a113b8-6e2a-49ca-a3ee-1b81afdf8834" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_0d996fe4-1adb-47f4-8cf2-7a7e85e45ec4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_2e50054e-d4bd-4858-8d2e-41484e2d9c35" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_93a113b8-6e2a-49ca-a3ee-1b81afdf8834" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_2e50054e-d4bd-4858-8d2e-41484e2d9c35" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_442154e6-7404-4d45-85e8-d285e48d5635" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2e50054e-d4bd-4858-8d2e-41484e2d9c35" xlink:to="loc_srt_ProductOrServiceAxis_442154e6-7404-4d45-85e8-d285e48d5635" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_442154e6-7404-4d45-85e8-d285e48d5635_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_442154e6-7404-4d45-85e8-d285e48d5635" xlink:to="loc_srt_ProductsAndServicesDomain_442154e6-7404-4d45-85e8-d285e48d5635_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6e7a3064-0370-48b3-adeb-8ff7e6fc8ad3" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_442154e6-7404-4d45-85e8-d285e48d5635" xlink:to="loc_srt_ProductsAndServicesDomain_6e7a3064-0370-48b3-adeb-8ff7e6fc8ad3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PlatformAndReferralFeesNetMember_a8629e56-43b5-4cff-9c26-adbe2ae1c1bb" xlink:href="upst-20220630.xsd#upst_PlatformAndReferralFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6e7a3064-0370-48b3-adeb-8ff7e6fc8ad3" xlink:to="loc_upst_PlatformAndReferralFeesNetMember_a8629e56-43b5-4cff-9c26-adbe2ae1c1bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingFeesNetMember_9d3655ec-921e-403c-b9da-b33363b73bcd" xlink:href="upst-20220630.xsd#upst_ServicingFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6e7a3064-0370-48b3-adeb-8ff7e6fc8ad3" xlink:to="loc_upst_ServicingFeesNetMember_9d3655ec-921e-403c-b9da-b33363b73bcd" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueNarrativeDetails" xlink:type="extended" id="i9d73edd1596f478c8eb3b7c47ecc913d_RevenueNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanPremiumFeesAndLoanTrailingFees_bf8456ce-a24e-4f29-9340-87ee8b94226b" xlink:href="upst-20220630.xsd#upst_LoanPremiumFeesAndLoanTrailingFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_upst_LoanPremiumFeesAndLoanTrailingFees_bf8456ce-a24e-4f29-9340-87ee8b94226b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilityAtFairValueAmount_ad06fc21-4b36-4107-b815-75d2fdd81cf0" xlink:href="upst-20220630.xsd#upst_TrailingFeeLiabilityAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_upst_TrailingFeeLiabilityAtFairValueAmount_ad06fc21-4b36-4107-b815-75d2fdd81cf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_3862ed0e-0369-45df-b5fb-c79e3af62e46" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_3862ed0e-0369-45df-b5fb-c79e3af62e46" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedFeesAndOtherRevenueReceivable_42ab6e6e-5497-457a-96b9-f0171243627b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedFeesAndOtherRevenueReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_AccruedFeesAndOtherRevenueReceivable_42ab6e6e-5497-457a-96b9-f0171243627b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_afa7dc1e-6b43-430e-88d1-6af8295e08f0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_afa7dc1e-6b43-430e-88d1-6af8295e08f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_4bf2da2f-8e6a-4104-b84e-71db54d44cd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_4bf2da2f-8e6a-4104-b84e-71db54d44cd2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_6a553775-51fa-4ed1-9ace-528f59664df1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_6a553775-51fa-4ed1-9ace-528f59664df1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_5aa3f9ca-edbc-4352-95b9-67559515495a" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_076e9914-7a4b-49f6-b752-a0ab9d832a27" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:to="loc_srt_ProductOrServiceAxis_076e9914-7a4b-49f6-b752-a0ab9d832a27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_076e9914-7a4b-49f6-b752-a0ab9d832a27_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_076e9914-7a4b-49f6-b752-a0ab9d832a27" xlink:to="loc_srt_ProductsAndServicesDomain_076e9914-7a4b-49f6-b752-a0ab9d832a27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a77fcefe-92f4-4340-b901-22468553d286" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_076e9914-7a4b-49f6-b752-a0ab9d832a27" xlink:to="loc_srt_ProductsAndServicesDomain_a77fcefe-92f4-4340-b901-22468553d286" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PlatformAndReferralFeesNetMember_55fa44e5-88b8-4f70-9812-7d2c022c3870" xlink:href="upst-20220630.xsd#upst_PlatformAndReferralFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a77fcefe-92f4-4340-b901-22468553d286" xlink:to="loc_upst_PlatformAndReferralFeesNetMember_55fa44e5-88b8-4f70-9812-7d2c022c3870" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_c4dc248a-871b-45b2-8680-8e8b176609e1" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:to="loc_srt_MajorCustomersAxis_c4dc248a-871b-45b2-8680-8e8b176609e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_c4dc248a-871b-45b2-8680-8e8b176609e1_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_c4dc248a-871b-45b2-8680-8e8b176609e1" xlink:to="loc_srt_NameOfMajorCustomerDomain_c4dc248a-871b-45b2-8680-8e8b176609e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_c4dc248a-871b-45b2-8680-8e8b176609e1" xlink:to="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerAMember_98162c62-870f-42b7-bb7f-f5f8e2c42545" xlink:href="upst-20220630.xsd#upst_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:to="loc_upst_CustomerAMember_98162c62-870f-42b7-bb7f-f5f8e2c42545" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerBMember_2203bf5e-ea37-44f8-b6c0-c0033d4613a8" xlink:href="upst-20220630.xsd#upst_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:to="loc_upst_CustomerBMember_2203bf5e-ea37-44f8-b6c0-c0033d4613a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerCMember_7f9c80e2-4e31-47d5-8ae0-9a916f8fa332" xlink:href="upst-20220630.xsd#upst_CustomerCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:to="loc_upst_CustomerCMember_7f9c80e2-4e31-47d5-8ae0-9a916f8fa332" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerDMember_d8130ba2-fcda-41c4-8b25-c2a09edfca0b" xlink:href="upst-20220630.xsd#upst_CustomerDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_a1a01230-da28-4abc-b489-654a9ce75d1d" xlink:to="loc_upst_CustomerDMember_d8130ba2-fcda-41c4-8b25-c2a09edfca0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_8ee4f107-2709-4076-925f-4e093374e2f5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_8ee4f107-2709-4076-925f-4e093374e2f5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_8ee4f107-2709-4076-925f-4e093374e2f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_8ee4f107-2709-4076-925f-4e093374e2f5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_8ee4f107-2709-4076-925f-4e093374e2f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_83aeb3f0-2f7d-4534-abb5-65fc5ed1e15c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_8ee4f107-2709-4076-925f-4e093374e2f5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_83aeb3f0-2f7d-4534-abb5-65fc5ed1e15c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_4f227b37-cb5c-4516-bb54-bfb084cffd92" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_83aeb3f0-2f7d-4534-abb5-65fc5ed1e15c" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_4f227b37-cb5c-4516-bb54-bfb084cffd92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3e330766-8f1f-4995-8cc8-4901a307aaaa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_4352e91c-0ed4-4a14-b0b6-f885156136de" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3e330766-8f1f-4995-8cc8-4901a307aaaa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_3e330766-8f1f-4995-8cc8-4901a307aaaa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3e330766-8f1f-4995-8cc8-4901a307aaaa" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_3e330766-8f1f-4995-8cc8-4901a307aaaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27a5eb15-2689-468e-a60a-aa24d3edbe2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3e330766-8f1f-4995-8cc8-4901a307aaaa" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27a5eb15-2689-468e-a60a-aa24d3edbe2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_4d040070-5453-4629-a5f1-bd8c7bec0671" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27a5eb15-2689-468e-a60a-aa24d3edbe2d" xlink:to="loc_us-gaap_SalesRevenueNetMember_4d040070-5453-4629-a5f1-bd8c7bec0671" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_300d37ed-fc9c-41de-9475-9790c12aa6e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27a5eb15-2689-468e-a60a-aa24d3edbe2d" xlink:to="loc_us-gaap_AccountsReceivableMember_300d37ed-fc9c-41de-9475-9790c12aa6e0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueFeesCollectedDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#RevenueFeesCollectedDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueFeesCollectedDetails" xlink:type="extended" id="i506f5a3e86a04263a5b93f17b09af99e_RevenueFeesCollectedDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_79df4b02-b489-44f4-902c-e3c87a8db874" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d0e7b712-2e1b-4483-a660-a23f802419a8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_79df4b02-b489-44f4-902c-e3c87a8db874" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d0e7b712-2e1b-4483-a660-a23f802419a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_d64fb8ea-a56b-4ba9-9d7d-4d2bd3b1293d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_79df4b02-b489-44f4-902c-e3c87a8db874" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_d64fb8ea-a56b-4ba9-9d7d-4d2bd3b1293d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_d64fb8ea-a56b-4ba9-9d7d-4d2bd3b1293d" xlink:to="loc_srt_ProductOrServiceAxis_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe" xlink:to="loc_srt_ProductsAndServicesDomain_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ce596a31-cd17-48cf-8e13-2d11cf2714f6" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_b5f7915a-a66d-48c0-84a8-cd1f6a8ba5fe" xlink:to="loc_srt_ProductsAndServicesDomain_ce596a31-cd17-48cf-8e13-2d11cf2714f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CollectionAgencyFeesMember_9629d2db-f5a9-4b5b-8cf7-1990de909e42" xlink:href="upst-20220630.xsd#upst_CollectionAgencyFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ce596a31-cd17-48cf-8e13-2d11cf2714f6" xlink:to="loc_upst_CollectionAgencyFeesMember_9629d2db-f5a9-4b5b-8cf7-1990de909e42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BorrowerFeesMember_8c429ee1-d53a-4443-af3e-55615efa2e3f" xlink:href="upst-20220630.xsd#upst_BorrowerFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ce596a31-cd17-48cf-8e13-2d11cf2714f6" xlink:to="loc_upst_BorrowerFeesMember_8c429ee1-d53a-4443-af3e-55615efa2e3f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/VariableInterestEntitiesAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#VariableInterestEntitiesAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/VariableInterestEntitiesAssetsandLiabilitiesDetails" xlink:type="extended" id="i8cb1b535e8194ec2b7ee105f9daedf18_VariableInterestEntitiesAssetsandLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_09262637-cc1d-420e-a8c3-8ec080d68285" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:to="loc_us-gaap_Assets_09262637-cc1d-420e-a8c3-8ec080d68285" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_c07c5c9c-5ca5-4280-84f2-796de307369f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:to="loc_us-gaap_Liabilities_c07c5c9c-5ca5-4280-84f2-796de307369f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_265049e1-5e15-45c1-a5e0-7262d5325338" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:to="loc_us-gaap_StockholdersEquity_265049e1-5e15-45c1-a5e0-7262d5325338" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_c7856215-d551-491e-98c1-5baac97c3c92" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:to="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_c7856215-d551-491e-98c1-5baac97c3c92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_fd1d4a40-59e3-44f3-bc06-41d6a72fc0d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_15b2785a-1aa3-4c7a-91bc-fadceef16baa" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_fd1d4a40-59e3-44f3-bc06-41d6a72fc0d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_0972cc87-a9ca-4338-afde-5e4722453eba" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_fd1d4a40-59e3-44f3-bc06-41d6a72fc0d2" xlink:to="loc_srt_ConsolidatedEntitiesAxis_0972cc87-a9ca-4338-afde-5e4722453eba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_0972cc87-a9ca-4338-afde-5e4722453eba_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0972cc87-a9ca-4338-afde-5e4722453eba" xlink:to="loc_srt_ConsolidatedEntitiesDomain_0972cc87-a9ca-4338-afde-5e4722453eba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_9dd0e836-aa72-41a7-8797-e84c61152842" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_0972cc87-a9ca-4338-afde-5e4722453eba" xlink:to="loc_srt_ConsolidatedEntitiesDomain_9dd0e836-aa72-41a7-8797-e84c61152842" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_9574a3d3-3101-4eb2-a581-c92ccae387af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_9dd0e836-aa72-41a7-8797-e84c61152842" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_9574a3d3-3101-4eb2-a581-c92ccae387af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_342ba9aa-e63a-4366-9bb0-9ac72bd83267" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_9dd0e836-aa72-41a7-8797-e84c61152842" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_342ba9aa-e63a-4366-9bb0-9ac72bd83267" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_9b53156d-452a-436d-a472-cc27c5d5da26" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_fd1d4a40-59e3-44f3-bc06-41d6a72fc0d2" xlink:to="loc_srt_CounterpartyNameAxis_9b53156d-452a-436d-a472-cc27c5d5da26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9b53156d-452a-436d-a472-cc27c5d5da26_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_9b53156d-452a-436d-a472-cc27c5d5da26" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9b53156d-452a-436d-a472-cc27c5d5da26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_d0184744-e1c6-4bad-8743-45c764ee7881" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_9b53156d-452a-436d-a472-cc27c5d5da26" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_d0184744-e1c6-4bad-8743-45c764ee7881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SecuritizationsMember_42f41691-8a21-45f6-9274-be479a16d456" xlink:href="upst-20220630.xsd#upst_SecuritizationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_d0184744-e1c6-4bad-8743-45c764ee7881" xlink:to="loc_upst_SecuritizationsMember_42f41691-8a21-45f6-9274-be479a16d456" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/VariableInterestEntitiesNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#VariableInterestEntitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/VariableInterestEntitiesNarrativeDetails" xlink:type="extended" id="idde1b31c5d204725824f5209abf750a9_VariableInterestEntitiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_af836911-d182-4769-a255-67876ab40865" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_6137b304-df45-4c31-b3f4-54de5e4deb3e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_af836911-d182-4769-a255-67876ab40865" xlink:to="loc_us-gaap_NotesReceivableNet_6137b304-df45-4c31-b3f4-54de5e4deb3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_fca17696-9961-4f91-8fcb-8ca228b46136" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_af836911-d182-4769-a255-67876ab40865" xlink:to="loc_us-gaap_RestrictedCash_fca17696-9961-4f91-8fcb-8ca228b46136" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2e2f19fe-8a23-407c-a095-e223d2cbe132" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_af836911-d182-4769-a255-67876ab40865" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2e2f19fe-8a23-407c-a095-e223d2cbe132" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_4b093197-66ec-4e33-80ae-81c7d95d77f7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2e2f19fe-8a23-407c-a095-e223d2cbe132" xlink:to="loc_srt_ConsolidatedEntitiesAxis_4b093197-66ec-4e33-80ae-81c7d95d77f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_4b093197-66ec-4e33-80ae-81c7d95d77f7_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_4b093197-66ec-4e33-80ae-81c7d95d77f7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_4b093197-66ec-4e33-80ae-81c7d95d77f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_be484c2e-a5d2-46f6-92a5-5c2c2e486c74" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_4b093197-66ec-4e33-80ae-81c7d95d77f7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_be484c2e-a5d2-46f6-92a5-5c2c2e486c74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_45ca1837-d857-48f9-9de5-fedaf335a366" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_be484c2e-a5d2-46f6-92a5-5c2c2e486c74" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_45ca1837-d857-48f9-9de5-fedaf335a366" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_006e2d41-47fa-4ec9-8f51-7752f07c8b3a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2e2f19fe-8a23-407c-a095-e223d2cbe132" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_006e2d41-47fa-4ec9-8f51-7752f07c8b3a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_006e2d41-47fa-4ec9-8f51-7752f07c8b3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_006e2d41-47fa-4ec9-8f51-7752f07c8b3a" xlink:to="loc_us-gaap_ReceivableTypeDomain_006e2d41-47fa-4ec9-8f51-7752f07c8b3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_ecc97573-a8e0-44ab-bb71-cfb3c1a26ca9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_006e2d41-47fa-4ec9-8f51-7752f07c8b3a" xlink:to="loc_us-gaap_ReceivableTypeDomain_ecc97573-a8e0-44ab-bb71-cfb3c1a26ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_NotesReceivableAndResidualCertificatesMember_e0d10a72-733d-4a8e-908b-156a35fb6684" xlink:href="upst-20220630.xsd#upst_NotesReceivableAndResidualCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_ecc97573-a8e0-44ab-bb71-cfb3c1a26ca9" xlink:to="loc_upst_NotesReceivableAndResidualCertificatesMember_e0d10a72-733d-4a8e-908b-156a35fb6684" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementAssetsandLiabilitiesDetails" xlink:type="extended" id="ie01fc528348b468bb8405786e2e013ef_FairValueMeasurementAssetsandLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_8e61901b-19dc-49f7-88f8-645bb686eaf0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_8e61901b-19dc-49f7-88f8-645bb686eaf0" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_58455f26-e35a-4a52-8161-19e95059b569" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_58455f26-e35a-4a52-8161-19e95059b569" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_ef0238ec-713d-4d74-a273-8ab628da7173" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_ef0238ec-713d-4d74-a273-8ab628da7173" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_644e51e5-50d1-4fb4-865e-848fc457eb76" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_644e51e5-50d1-4fb4-865e-848fc457eb76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_c6b8ead3-69cb-4d91-bd0b-5fcf1afaaf66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_cbc06ccf-b837-4682-bf8e-6028f3c36a58" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_c6b8ead3-69cb-4d91-bd0b-5fcf1afaaf66" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_0179f6d2-6b79-46cc-b43c-15cb59af458a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_8e61901b-19dc-49f7-88f8-645bb686eaf0" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_0179f6d2-6b79-46cc-b43c-15cb59af458a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_ad7c1887-6aec-4f04-a460-9c91a8a3d224" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_0179f6d2-6b79-46cc-b43c-15cb59af458a" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_ad7c1887-6aec-4f04-a460-9c91a8a3d224" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_c1a5a7b1-e2f3-4968-b100-5c58995e5607" xlink:href="upst-20220630.xsd#upst_TrailingFeeLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_0179f6d2-6b79-46cc-b43c-15cb59af458a" xlink:to="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_c1a5a7b1-e2f3-4968-b100-5c58995e5607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_19357153-d11c-430a-92b2-44657922a2d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_0179f6d2-6b79-46cc-b43c-15cb59af458a" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_19357153-d11c-430a-92b2-44657922a2d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_efe037e8-f682-45d8-af1a-c6561bb30a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_8e61901b-19dc-49f7-88f8-645bb686eaf0" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_efe037e8-f682-45d8-af1a-c6561bb30a8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_91277f52-8b7e-4351-9050-187557bd0ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_efe037e8-f682-45d8-af1a-c6561bb30a8e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_91277f52-8b7e-4351-9050-187557bd0ce4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_91277f52-8b7e-4351-9050-187557bd0ce4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_91277f52-8b7e-4351-9050-187557bd0ce4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_91277f52-8b7e-4351-9050-187557bd0ce4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c3cce263-b59a-4d13-ba7b-57644a04a066" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_91277f52-8b7e-4351-9050-187557bd0ce4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c3cce263-b59a-4d13-ba7b-57644a04a066" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_f267f11c-5a50-4597-abe5-ed8851b05f74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c3cce263-b59a-4d13-ba7b-57644a04a066" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_f267f11c-5a50-4597-abe5-ed8851b05f74" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementNarrativeDetails" xlink:type="extended" id="icd40707d044942c493b7b5a6f337e247_FairValueMeasurementNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_ca1cd2ec-2a3c-469a-8bfb-dadf5ac14a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_ca1cd2ec-2a3c-469a-8bfb-dadf5ac14a6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansHeldForInvestmentFairValueDisclosure_30944042-244a-4a52-8124-a88b95f7032b" xlink:href="upst-20220630.xsd#upst_LoansHeldForInvestmentFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_upst_LoansHeldForInvestmentFairValueDisclosure_30944042-244a-4a52-8124-a88b95f7032b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_a8e8c155-f70f-42f9-8bcd-4d1770a28b57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_a8e8c155-f70f-42f9-8bcd-4d1770a28b57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage_251bb439-1555-4e16-8541-823a54a76f67" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage_251bb439-1555-4e16-8541-823a54a76f67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage_474fb466-552c-46dd-b0ed-b20606f2622f" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage_474fb466-552c-46dd-b0ed-b20606f2622f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage_2a377e4a-86c8-46af-b7f4-9cd4deaa9fd3" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage_2a377e4a-86c8-46af-b7f4-9cd4deaa9fd3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeesLiabilityMeasurementInput_b8884224-2210-4fc5-97b0-ec61ab861025" xlink:href="upst-20220630.xsd#upst_TrailingFeesLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_upst_TrailingFeesLiabilityMeasurementInput_b8884224-2210-4fc5-97b0-ec61ab861025" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_9e2796fa-42b0-441c-a804-c975e9e5654e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableThresholdPeriodPastDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_9e2796fa-42b0-441c-a804-c975e9e5654e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff_efb1d6d8-8f27-4df4-b05b-4e379aaa8cff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff_efb1d6d8-8f27-4df4-b05b-4e379aaa8cff" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_043edde1-7ae2-4429-a7a4-89860990843b" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_99ace206-ec53-4cde-b535-b7eeab6842c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_99ace206-ec53-4cde-b535-b7eeab6842c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_99ace206-ec53-4cde-b535-b7eeab6842c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_99ace206-ec53-4cde-b535-b7eeab6842c7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_99ace206-ec53-4cde-b535-b7eeab6842c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9978e92d-b82f-4884-bba2-363298ba1cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_99ace206-ec53-4cde-b535-b7eeab6842c7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9978e92d-b82f-4884-bba2-363298ba1cd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_d7378b5b-a81d-44a5-ba04-04a987b6c2ca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9978e92d-b82f-4884-bba2-363298ba1cd4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_d7378b5b-a81d-44a5-ba04-04a987b6c2ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a517abe2-1e82-4527-a978-bd9bd7aa259c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:to="loc_srt_RangeAxis_a517abe2-1e82-4527-a978-bd9bd7aa259c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a517abe2-1e82-4527-a978-bd9bd7aa259c_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a517abe2-1e82-4527-a978-bd9bd7aa259c" xlink:to="loc_srt_RangeMember_a517abe2-1e82-4527-a978-bd9bd7aa259c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8d6cfe65-c087-4a99-b1a0-cfc5f1e52ef2" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a517abe2-1e82-4527-a978-bd9bd7aa259c" xlink:to="loc_srt_RangeMember_8d6cfe65-c087-4a99-b1a0-cfc5f1e52ef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_35b53ee2-5502-4ea5-8b79-921486675e1a" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8d6cfe65-c087-4a99-b1a0-cfc5f1e52ef2" xlink:to="loc_srt_MinimumMember_35b53ee2-5502-4ea5-8b79-921486675e1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3037b789-8017-4773-a282-6f10faa841ef" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8d6cfe65-c087-4a99-b1a0-cfc5f1e52ef2" xlink:to="loc_srt_MaximumMember_3037b789-8017-4773-a282-6f10faa841ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_1b997c7c-184d-4f36-9770-4d1a9d2de72f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_b1172fcf-1c38-4cef-b4a7-a437e1e1e6c7" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_1b997c7c-184d-4f36-9770-4d1a9d2de72f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_ee0d0dd7-ab8c-449a-8bd1-43709a8c94fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_1b997c7c-184d-4f36-9770-4d1a9d2de72f" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_ee0d0dd7-ab8c-449a-8bd1-43709a8c94fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputEntityCreditRiskMember_4ab73ab1-d78d-4ab9-b014-8356c7824234" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputEntityCreditRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_1b997c7c-184d-4f36-9770-4d1a9d2de72f" xlink:to="loc_us-gaap_MeasurementInputEntityCreditRiskMember_4ab73ab1-d78d-4ab9-b014-8356c7824234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_35c07c66-79cd-4164-90a4-aa6772f3aceb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_35c07c66-79cd-4164-90a4-aa6772f3aceb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_35c07c66-79cd-4164-90a4-aa6772f3aceb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_35c07c66-79cd-4164-90a4-aa6772f3aceb" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_35c07c66-79cd-4164-90a4-aa6772f3aceb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cfa92e78-c404-40f4-8d1e-376eb0017992" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_35c07c66-79cd-4164-90a4-aa6772f3aceb" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cfa92e78-c404-40f4-8d1e-376eb0017992" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableMember_b97f4265-e82b-433f-8815-a7f32926cb6b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cfa92e78-c404-40f4-8d1e-376eb0017992" xlink:to="loc_us-gaap_NotesReceivableMember_b97f4265-e82b-433f-8815-a7f32926cb6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_0b27292a-f35b-4b23-b8d1-a3c359bfb251" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cfa92e78-c404-40f4-8d1e-376eb0017992" xlink:to="loc_us-gaap_LoansReceivableMember_0b27292a-f35b-4b23-b8d1-a3c359bfb251" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_e1318911-66c9-41ae-b6ed-a30e6b621a3a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c25ac75d-5c5e-4d38-8f8b-f9a118d3b0cd" xlink:to="loc_us-gaap_ValuationTechniqueAxis_e1318911-66c9-41ae-b6ed-a30e6b621a3a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_e1318911-66c9-41ae-b6ed-a30e6b621a3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_e1318911-66c9-41ae-b6ed-a30e6b621a3a" xlink:to="loc_us-gaap_ValuationTechniqueDomain_e1318911-66c9-41ae-b6ed-a30e6b621a3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_affd7b1a-649a-4bb9-be06-9b7fd7c62ec9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_e1318911-66c9-41ae-b6ed-a30e6b621a3a" xlink:to="loc_us-gaap_ValuationTechniqueDomain_affd7b1a-649a-4bb9-be06-9b7fd7c62ec9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_5bef9490-29f7-40ca-bf48-52a5a783d9cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_affd7b1a-649a-4bb9-be06-9b7fd7c62ec9" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_5bef9490-29f7-40ca-bf48-52a5a783d9cd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementSignificantInputsandAssumptionsDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementSignificantInputsandAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementSignificantInputsandAssumptionsDetails" xlink:type="extended" id="ie24a5f37772f41b892c802a5d1ae5d2b_FairValueMeasurementSignificantInputsandAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_34e8d1e9-a143-43e9-be55-6f8911fb317e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansReceivableMeasurementInput_5b581572-ca76-4159-847b-d62e399ebbc2" xlink:href="upst-20220630.xsd#upst_LoansReceivableMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_34e8d1e9-a143-43e9-be55-6f8911fb317e" xlink:to="loc_upst_LoansReceivableMeasurementInput_5b581572-ca76-4159-847b-d62e399ebbc2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_34e8d1e9-a143-43e9-be55-6f8911fb317e" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6d8948d4-b3b0-40e5-88a3-004fd00e5173" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:to="loc_srt_RangeAxis_6d8948d4-b3b0-40e5-88a3-004fd00e5173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6d8948d4-b3b0-40e5-88a3-004fd00e5173_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6d8948d4-b3b0-40e5-88a3-004fd00e5173" xlink:to="loc_srt_RangeMember_6d8948d4-b3b0-40e5-88a3-004fd00e5173_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c1b949eb-a622-42f8-8d57-e2fa153f8ff4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6d8948d4-b3b0-40e5-88a3-004fd00e5173" xlink:to="loc_srt_RangeMember_c1b949eb-a622-42f8-8d57-e2fa153f8ff4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_ffa7b03d-8870-45fb-a22c-37b5a1684167" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c1b949eb-a622-42f8-8d57-e2fa153f8ff4" xlink:to="loc_srt_MinimumMember_ffa7b03d-8870-45fb-a22c-37b5a1684167" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_bc5a8378-18b1-4fc2-87fa-c737c5071fdd" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c1b949eb-a622-42f8-8d57-e2fa153f8ff4" xlink:to="loc_srt_MaximumMember_bc5a8378-18b1-4fc2-87fa-c737c5071fdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_ba123195-728d-4661-9fe4-05bb303bcbc6" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c1b949eb-a622-42f8-8d57-e2fa153f8ff4" xlink:to="loc_srt_WeightedAverageMember_ba123195-728d-4661-9fe4-05bb303bcbc6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_92587f51-f367-42b2-b769-6bd21eecf5e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:to="loc_us-gaap_ValuationTechniqueAxis_92587f51-f367-42b2-b769-6bd21eecf5e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_92587f51-f367-42b2-b769-6bd21eecf5e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_92587f51-f367-42b2-b769-6bd21eecf5e4" xlink:to="loc_us-gaap_ValuationTechniqueDomain_92587f51-f367-42b2-b769-6bd21eecf5e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_8516890e-3594-413a-9e0b-35e6f0afd7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_92587f51-f367-42b2-b769-6bd21eecf5e4" xlink:to="loc_us-gaap_ValuationTechniqueDomain_8516890e-3594-413a-9e0b-35e6f0afd7e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_b9826067-cfc9-41d9-a88f-4e39c66751f5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_8516890e-3594-413a-9e0b-35e6f0afd7e8" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_b9826067-cfc9-41d9-a88f-4e39c66751f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c4e2775b-dd59-465d-abdb-5595d8c6e693" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c4e2775b-dd59-465d-abdb-5595d8c6e693" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c4e2775b-dd59-465d-abdb-5595d8c6e693_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c4e2775b-dd59-465d-abdb-5595d8c6e693" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c4e2775b-dd59-465d-abdb-5595d8c6e693_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdbe76cc-0e02-4985-9c1b-182bfca67ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c4e2775b-dd59-465d-abdb-5595d8c6e693" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdbe76cc-0e02-4985-9c1b-182bfca67ccc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_a55aabaf-9bce-4c41-bd88-3cca2192636c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdbe76cc-0e02-4985-9c1b-182bfca67ccc" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_a55aabaf-9bce-4c41-bd88-3cca2192636c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_63180225-1888-48df-a291-b37af5f832be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_63180225-1888-48df-a291-b37af5f832be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_63180225-1888-48df-a291-b37af5f832be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_63180225-1888-48df-a291-b37af5f832be" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_63180225-1888-48df-a291-b37af5f832be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_c017ede9-cfa0-4c9c-8bb2-351ffc1e24c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_63180225-1888-48df-a291-b37af5f832be" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_c017ede9-cfa0-4c9c-8bb2-351ffc1e24c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_6a641f7e-ad00-4336-9f99-13d495e48b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_c017ede9-cfa0-4c9c-8bb2-351ffc1e24c4" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_6a641f7e-ad00-4336-9f99-13d495e48b0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputEntityCreditRiskMember_c718c0bc-447f-45cb-b86c-e118cfb38de1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputEntityCreditRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_c017ede9-cfa0-4c9c-8bb2-351ffc1e24c4" xlink:to="loc_us-gaap_MeasurementInputEntityCreditRiskMember_c718c0bc-447f-45cb-b86c-e118cfb38de1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPrepaymentRateMember_6bedb492-de1d-4678-bb6b-6b8f3bfa2b75" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputPrepaymentRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_c017ede9-cfa0-4c9c-8bb2-351ffc1e24c4" xlink:to="loc_us-gaap_MeasurementInputPrepaymentRateMember_6bedb492-de1d-4678-bb6b-6b8f3bfa2b75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_bd77224c-35f4-4c27-9f25-1e8157d03052" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_8abb458d-17e1-435c-9adb-844a79cef067" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_bd77224c-35f4-4c27-9f25-1e8157d03052" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bd77224c-35f4-4c27-9f25-1e8157d03052_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_bd77224c-35f4-4c27-9f25-1e8157d03052" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bd77224c-35f4-4c27-9f25-1e8157d03052_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8ae1bb1d-840c-4185-bef6-c7b5cdd6dd78" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_bd77224c-35f4-4c27-9f25-1e8157d03052" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8ae1bb1d-840c-4185-bef6-c7b5cdd6dd78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_a81f2ed6-c6c2-4c95-a068-6de81a9eb4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8ae1bb1d-840c-4185-bef6-c7b5cdd6dd78" xlink:to="loc_us-gaap_LoansReceivableMember_a81f2ed6-c6c2-4c95-a068-6de81a9eb4fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableMember_b0be1898-97b4-4fd6-a505-da87dc5450fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8ae1bb1d-840c-4185-bef6-c7b5cdd6dd78" xlink:to="loc_us-gaap_NotesReceivableMember_b0be1898-97b4-4fd6-a505-da87dc5450fd" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementSensitivityofFairValueDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementSensitivityofFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementSensitivityofFairValueDetails" xlink:type="extended" id="i67a5d5c12f59418c94dc490059a7b9e1_FairValueMeasurementSensitivityofFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_197bf2e9-dcb0-4675-aaf3-a61e27af9850" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_197bf2e9-dcb0-4675-aaf3-a61e27af9850" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DiscountRateAbstract_3cdc29b7-9c2f-49ed-af28-acfc4a473072" xlink:href="upst-20220630.xsd#upst_DiscountRateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:to="loc_upst_DiscountRateAbstract_3cdc29b7-9c2f-49ed-af28-acfc4a473072" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates_f0af3fed-ae59-4ae5-900b-7317fbb7a832" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DiscountRateAbstract_3cdc29b7-9c2f-49ed-af28-acfc4a473072" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates_f0af3fed-ae59-4ae5-900b-7317fbb7a832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates_5743a68f-63b6-49a3-bda2-a35c2bb888b0" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DiscountRateAbstract_3cdc29b7-9c2f-49ed-af28-acfc4a473072" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates_5743a68f-63b6-49a3-bda2-a35c2bb888b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ExpectedCreditLossRateAbstract_16ac65d9-1517-45c7-abb9-ae65d7284d61" xlink:href="upst-20220630.xsd#upst_ExpectedCreditLossRateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:to="loc_upst_ExpectedCreditLossRateAbstract_16ac65d9-1517-45c7-abb9-ae65d7284d61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates_74ad3eca-5a95-457a-b2e8-22b3842bf45e" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedCreditLossRateAbstract_16ac65d9-1517-45c7-abb9-ae65d7284d61" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates_74ad3eca-5a95-457a-b2e8-22b3842bf45e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates_a0f3c688-8c07-4bc8-9e12-53ddb5cf62df" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedCreditLossRateAbstract_16ac65d9-1517-45c7-abb9-ae65d7284d61" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates_a0f3c688-8c07-4bc8-9e12-53ddb5cf62df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ExpectedPrepaymentRateAbstract_dd2d4821-2871-4ca5-b04e-ea816042036c" xlink:href="upst-20220630.xsd#upst_ExpectedPrepaymentRateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:to="loc_upst_ExpectedPrepaymentRateAbstract_dd2d4821-2871-4ca5-b04e-ea816042036c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates_9758ac4a-b399-4530-82af-8623560146b8" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedPrepaymentRateAbstract_dd2d4821-2871-4ca5-b04e-ea816042036c" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates_9758ac4a-b399-4530-82af-8623560146b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates_6e8a1f40-8baf-4015-88d7-582728450d61" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedPrepaymentRateAbstract_dd2d4821-2871-4ca5-b04e-ea816042036c" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates_6e8a1f40-8baf-4015-88d7-582728450d61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_a0ace3b9-9033-4145-a2a2-527936688c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_2c99fd44-3b85-4e4b-88b8-9f763203c011" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_a0ace3b9-9033-4145-a2a2-527936688c0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f05e349d-ff78-4d01-bf87-3f3e919bc55c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_a0ace3b9-9033-4145-a2a2-527936688c0d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f05e349d-ff78-4d01-bf87-3f3e919bc55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f05e349d-ff78-4d01-bf87-3f3e919bc55c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f05e349d-ff78-4d01-bf87-3f3e919bc55c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f05e349d-ff78-4d01-bf87-3f3e919bc55c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_208a463c-c8cc-45fc-be30-f013157525b8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f05e349d-ff78-4d01-bf87-3f3e919bc55c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_208a463c-c8cc-45fc-be30-f013157525b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_0b40833c-59c3-4423-8258-a61445d87a52" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_208a463c-c8cc-45fc-be30-f013157525b8" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_0b40833c-59c3-4423-8258-a61445d87a52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_2552a4e6-f12c-408a-adce-7a2bfea1b43c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_a0ace3b9-9033-4145-a2a2-527936688c0d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_2552a4e6-f12c-408a-adce-7a2bfea1b43c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2552a4e6-f12c-408a-adce-7a2bfea1b43c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_2552a4e6-f12c-408a-adce-7a2bfea1b43c" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2552a4e6-f12c-408a-adce-7a2bfea1b43c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_5c32dfde-8d41-4c33-9d3b-2156b704b004" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_2552a4e6-f12c-408a-adce-7a2bfea1b43c" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_5c32dfde-8d41-4c33-9d3b-2156b704b004" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_d9788517-6b42-431d-8e7e-ee969eff4d8f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_5c32dfde-8d41-4c33-9d3b-2156b704b004" xlink:to="loc_us-gaap_LoansReceivableMember_d9788517-6b42-431d-8e7e-ee969eff4d8f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoansRollforwardDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementLoansRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoansRollforwardDetails" xlink:type="extended" id="i34e078aaafe646648f26138d181711d4_FairValueMeasurementLoansRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_6c673c17-6bc1-4ce5-8bce-bf5d57b3eb1b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_6c673c17-6bc1-4ce5-8bce-bf5d57b3eb1b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_c7114995-4e42-4e5e-ba27-807bda4fa91f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_c7114995-4e42-4e5e-ba27-807bda4fa91f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification_62b8f447-06a9-4528-ac51-7483581b1f0f" xlink:href="upst-20220630.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification_62b8f447-06a9-4528-ac51-7483581b1f0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_8a4bc73d-e0c9-4de8-bf89-82e204e5e2f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_8a4bc73d-e0c9-4de8-bf89-82e204e5e2f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_82e3f3fe-5ad9-458e-9399-75b4f665a96d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_82e3f3fe-5ad9-458e-9399-75b4f665a96d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors_84626028-a02d-4586-8005-37f4a0187690" xlink:href="upst-20220630.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors_84626028-a02d-4586-8005-37f4a0187690" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors_c96c63ae-ed89-4b53-b317-104a2bf032f5" xlink:href="upst-20220630.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors_c96c63ae-ed89-4b53-b317-104a2bf032f5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived_6556792d-d33e-4db8-bb7c-00d17146c7e4" xlink:href="upst-20220630.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived_6556792d-d33e-4db8-bb7c-00d17146c7e4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_4ad25ad6-0e47-47ca-b331-5cde1ab524c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_4ad25ad6-0e47-47ca-b331-5cde1ab524c4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease_a717d427-74d9-491a-93c3-41e00ec988c8" xlink:href="upst-20220630.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_a7ec08c7-a277-4f55-9f9f-095383e0685e" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease_a717d427-74d9-491a-93c3-41e00ec988c8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_4b9257f5-7f5b-48b5-8a30-dac6855925e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ecf233fa-a1b9-4d28-923a-ee447184c91f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_6c673c17-6bc1-4ce5-8bce-bf5d57b3eb1b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ecf233fa-a1b9-4d28-923a-ee447184c91f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_c4bd4332-a904-4e2c-8e09-b7569f4cb13b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ecf233fa-a1b9-4d28-923a-ee447184c91f" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_c4bd4332-a904-4e2c-8e09-b7569f4cb13b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_c4bd4332-a904-4e2c-8e09-b7569f4cb13b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_c4bd4332-a904-4e2c-8e09-b7569f4cb13b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_c4bd4332-a904-4e2c-8e09-b7569f4cb13b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ed3bee1-09b6-46a4-baea-ee5229bf71b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_c4bd4332-a904-4e2c-8e09-b7569f4cb13b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ed3bee1-09b6-46a4-baea-ee5229bf71b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_cef8732c-b1ad-41e7-b7af-3f90edd8e15e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ed3bee1-09b6-46a4-baea-ee5229bf71b5" xlink:to="loc_us-gaap_LoansReceivableMember_cef8732c-b1ad-41e7-b7af-3f90edd8e15e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanHeldForSaleMember_3dfbbbcf-f48d-4ff5-bcc3-becae6e9d2fb" xlink:href="upst-20220630.xsd#upst_LoanHeldForSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoansReceivableMember_cef8732c-b1ad-41e7-b7af-3f90edd8e15e" xlink:to="loc_upst_LoanHeldForSaleMember_3dfbbbcf-f48d-4ff5-bcc3-becae6e9d2fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansHeldForInvestmentMember_80046f6b-40de-4ec4-8e82-adeb618168a4" xlink:href="upst-20220630.xsd#upst_LoansHeldForInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoansReceivableMember_cef8732c-b1ad-41e7-b7af-3f90edd8e15e" xlink:to="loc_upst_LoansHeldForInvestmentMember_80046f6b-40de-4ec4-8e82-adeb618168a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cbaec79-fc18-42de-854a-35f9c0b2ae71" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ecf233fa-a1b9-4d28-923a-ee447184c91f" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cbaec79-fc18-42de-854a-35f9c0b2ae71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9cbaec79-fc18-42de-854a-35f9c0b2ae71_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cbaec79-fc18-42de-854a-35f9c0b2ae71" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9cbaec79-fc18-42de-854a-35f9c0b2ae71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f4916c80-ea12-4a56-9426-d776f8639881" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cbaec79-fc18-42de-854a-35f9c0b2ae71" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f4916c80-ea12-4a56-9426-d776f8639881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_952fda2a-f4ac-4e31-8a04-ad4c6247d894" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f4916c80-ea12-4a56-9426-d776f8639881" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_952fda2a-f4ac-4e31-8a04-ad4c6247d894" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoansatFairValueDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementLoansatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoansatFairValueDetails" xlink:type="extended" id="i1d300d426cec49eeaffd72f6e4775e2c_FairValueMeasurementLoansatFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_ac9c7be5-5247-440e-9662-8969052dd50d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_b8b92568-28d9-4fc6-87be-930b7c624f88" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_ac9c7be5-5247-440e-9662-8969052dd50d" xlink:to="loc_us-gaap_NotesReceivableGross_b8b92568-28d9-4fc6-87be-930b7c624f88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_19185466-338b-48a9-99eb-685a345527ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_ac9c7be5-5247-440e-9662-8969052dd50d" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_19185466-338b-48a9-99eb-685a345527ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_a55244eb-93f6-4a63-81a7-14e65a1f1770" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_ac9c7be5-5247-440e-9662-8969052dd50d" xlink:to="loc_us-gaap_NotesReceivableNet_a55244eb-93f6-4a63-81a7-14e65a1f1770" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_43d3314b-fb08-4fdb-b321-40a01c344dba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_ac9c7be5-5247-440e-9662-8969052dd50d" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_43d3314b-fb08-4fdb-b321-40a01c344dba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_58cbf8b4-f744-4323-9757-8ae2a1c7e596" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_43d3314b-fb08-4fdb-b321-40a01c344dba" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_58cbf8b4-f744-4323-9757-8ae2a1c7e596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_58cbf8b4-f744-4323-9757-8ae2a1c7e596_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_58cbf8b4-f744-4323-9757-8ae2a1c7e596" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_58cbf8b4-f744-4323-9757-8ae2a1c7e596_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_aeeb10e1-a9fe-4311-8503-6c19e726e61f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_58cbf8b4-f744-4323-9757-8ae2a1c7e596" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_aeeb10e1-a9fe-4311-8503-6c19e726e61f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_d5ee54f2-ff2d-4b72-9809-9e5d15e98ac1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_aeeb10e1-a9fe-4311-8503-6c19e726e61f" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_d5ee54f2-ff2d-4b72-9809-9e5d15e98ac1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a82a6236-44f2-4cb3-964b-c531d387cb5e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_43d3314b-fb08-4fdb-b321-40a01c344dba" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a82a6236-44f2-4cb3-964b-c531d387cb5e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_a82a6236-44f2-4cb3-964b-c531d387cb5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a82a6236-44f2-4cb3-964b-c531d387cb5e" xlink:to="loc_us-gaap_ReceivableTypeDomain_a82a6236-44f2-4cb3-964b-c531d387cb5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_ce1a9cc8-7a51-43c8-af17-9eb1b46e4ebc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a82a6236-44f2-4cb3-964b-c531d387cb5e" xlink:to="loc_us-gaap_ReceivableTypeDomain_ce1a9cc8-7a51-43c8-af17-9eb1b46e4ebc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_8bc2d598-a4d0-4f36-9bf2-6540008928bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_ce1a9cc8-7a51-43c8-af17-9eb1b46e4ebc" xlink:to="loc_us-gaap_LoansReceivableMember_8bc2d598-a4d0-4f36-9bf2-6540008928bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_2f547fdd-338a-4496-8c4b-437c051dc6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_43d3314b-fb08-4fdb-b321-40a01c344dba" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_2f547fdd-338a-4496-8c4b-437c051dc6d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_2f547fdd-338a-4496-8c4b-437c051dc6d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_2f547fdd-338a-4496-8c4b-437c051dc6d8" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_2f547fdd-338a-4496-8c4b-437c051dc6d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a84eea9f-bb14-4c9a-ac30-67623fe56717" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_2f547fdd-338a-4496-8c4b-437c051dc6d8" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a84eea9f-bb14-4c9a-ac30-67623fe56717" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AutoLoansMember_f186560f-bc6c-455d-8a56-b4d18bfdb7d5" xlink:href="upst-20220630.xsd#upst_AutoLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a84eea9f-bb14-4c9a-ac30-67623fe56717" xlink:to="loc_upst_AutoLoansMember_f186560f-bc6c-455d-8a56-b4d18bfdb7d5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementNoteReceivableRollforwardDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementNoteReceivableRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementNoteReceivableRollforwardDetails" xlink:type="extended" id="id88f22884ddc456fba53aeaa98af883a_FairValueMeasurementNoteReceivableRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_c21019db-7c74-4518-b0e9-cc3bcfb4856d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_122d31a8-3d6a-4e76-bc81-850a1cf53d57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_c21019db-7c74-4518-b0e9-cc3bcfb4856d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_122d31a8-3d6a-4e76-bc81-850a1cf53d57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_669178a2-f260-44ac-a1de-b785a7705f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_122d31a8-3d6a-4e76-bc81-850a1cf53d57" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_669178a2-f260-44ac-a1de-b785a7705f7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_aa892149-c4d6-48f9-982d-8b99b78b29d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_122d31a8-3d6a-4e76-bc81-850a1cf53d57" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_aa892149-c4d6-48f9-982d-8b99b78b29d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_78666012-3007-4c98-a90a-ece078fa698b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_122d31a8-3d6a-4e76-bc81-850a1cf53d57" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_78666012-3007-4c98-a90a-ece078fa698b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_b61aed8d-30be-4b61-bb92-d4a85f0126d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_7e17c4ea-b2ce-4177-b090-16092574765a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_c21019db-7c74-4518-b0e9-cc3bcfb4856d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_7e17c4ea-b2ce-4177-b090-16092574765a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_fa7062f9-6d88-49af-8ced-ed4d81369335" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_7e17c4ea-b2ce-4177-b090-16092574765a" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_fa7062f9-6d88-49af-8ced-ed4d81369335" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_fa7062f9-6d88-49af-8ced-ed4d81369335_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_fa7062f9-6d88-49af-8ced-ed4d81369335" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_fa7062f9-6d88-49af-8ced-ed4d81369335_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3072348a-c18b-4781-b0ab-065a0094f9ea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_fa7062f9-6d88-49af-8ced-ed4d81369335" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3072348a-c18b-4781-b0ab-065a0094f9ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_NotesReceivableAndResidualCertificatesMember_17b4586c-119c-4679-aa7c-6a12de6e5bfe" xlink:href="upst-20220630.xsd#upst_NotesReceivableAndResidualCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3072348a-c18b-4781-b0ab-065a0094f9ea" xlink:to="loc_upst_NotesReceivableAndResidualCertificatesMember_17b4586c-119c-4679-aa7c-6a12de6e5bfe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_89776451-7011-42a6-8ccd-befd93f125da" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_7e17c4ea-b2ce-4177-b090-16092574765a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_89776451-7011-42a6-8ccd-befd93f125da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_89776451-7011-42a6-8ccd-befd93f125da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_89776451-7011-42a6-8ccd-befd93f125da" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_89776451-7011-42a6-8ccd-befd93f125da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7df3b05b-a0fe-4fc4-bd4e-0c019e90d2e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_89776451-7011-42a6-8ccd-befd93f125da" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7df3b05b-a0fe-4fc4-bd4e-0c019e90d2e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_11dafd63-5cf3-4993-8d5d-b91ea28e7aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7df3b05b-a0fe-4fc4-bd4e-0c019e90d2e0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_11dafd63-5cf3-4993-8d5d-b91ea28e7aaf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementFairValueAssumptionsDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementFairValueAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementFairValueAssumptionsDetails" xlink:type="extended" id="i0214aca453b343998ac053642c4f420e_FairValueMeasurementFairValueAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate_2bdafa23-64b2-48af-bf32-af8e7382eea6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate_2bdafa23-64b2-48af-bf32-af8e7382eea6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesExpectedCreditLosses_387c4971-4587-440e-9af2-bd900d8385be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesExpectedCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesExpectedCreditLosses_387c4971-4587-440e-9af2-bd900d8385be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate_6e185a41-43a0-45fb-b734-1ac1d61c65a3" xlink:href="upst-20220630.xsd#upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:to="loc_upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate_6e185a41-43a0-45fb-b734-1ac1d61c65a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed_970f42d7-41b8-4ce4-bd0f-8fee2d50f249" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed_970f42d7-41b8-4ce4-bd0f-8fee2d50f249" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_7534ff4d-eabf-468f-9ebe-d91ee01c611e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_3673a78f-a9c1-4545-8716-b206457e7f67" xlink:to="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_7534ff4d-eabf-468f-9ebe-d91ee01c611e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_7534ff4d-eabf-468f-9ebe-d91ee01c611e" xlink:to="loc_srt_RangeAxis_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7" xlink:to="loc_srt_RangeMember_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ffa5428b-7266-4e34-8aff-13ee96cef9d7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_34b8e0dc-e948-4fd7-847a-dd96aa7ef8e7" xlink:to="loc_srt_RangeMember_ffa5428b-7266-4e34-8aff-13ee96cef9d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_37fd6adb-795d-4235-bba8-90cb35ea3f2d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ffa5428b-7266-4e34-8aff-13ee96cef9d7" xlink:to="loc_srt_MinimumMember_37fd6adb-795d-4235-bba8-90cb35ea3f2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_25b7f433-a6e9-4a72-9b88-04eda3be0a4b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ffa5428b-7266-4e34-8aff-13ee96cef9d7" xlink:to="loc_srt_MaximumMember_25b7f433-a6e9-4a72-9b88-04eda3be0a4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_16613d6b-cec7-404e-9e92-1d4b4a6635ea" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ffa5428b-7266-4e34-8aff-13ee96cef9d7" xlink:to="loc_srt_WeightedAverageMember_16613d6b-cec7-404e-9e92-1d4b4a6635ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_407d903f-2370-4b65-bd35-96fd17274890" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_7534ff4d-eabf-468f-9ebe-d91ee01c611e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_407d903f-2370-4b65-bd35-96fd17274890" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_407d903f-2370-4b65-bd35-96fd17274890_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_407d903f-2370-4b65-bd35-96fd17274890" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_407d903f-2370-4b65-bd35-96fd17274890_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b88896ce-de23-4a27-8155-7cb7c8fee4e7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_407d903f-2370-4b65-bd35-96fd17274890" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b88896ce-de23-4a27-8155-7cb7c8fee4e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_8c9c52c0-52ab-4ed5-9ae1-443fd0fc3ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b88896ce-de23-4a27-8155-7cb7c8fee4e7" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_8c9c52c0-52ab-4ed5-9ae1-443fd0fc3ab3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_eb1f4dd6-970f-4d20-9ed5-d997d31f7222" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_7534ff4d-eabf-468f-9ebe-d91ee01c611e" xlink:to="loc_us-gaap_ValuationTechniqueAxis_eb1f4dd6-970f-4d20-9ed5-d997d31f7222" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_eb1f4dd6-970f-4d20-9ed5-d997d31f7222_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_eb1f4dd6-970f-4d20-9ed5-d997d31f7222" xlink:to="loc_us-gaap_ValuationTechniqueDomain_eb1f4dd6-970f-4d20-9ed5-d997d31f7222_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_aa97acfc-f2c6-49c4-b2c8-52768f0b0764" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_eb1f4dd6-970f-4d20-9ed5-d997d31f7222" xlink:to="loc_us-gaap_ValuationTechniqueDomain_aa97acfc-f2c6-49c4-b2c8-52768f0b0764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_a9088c78-1da7-48ba-aab8-d70d4eefa590" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_aa97acfc-f2c6-49c4-b2c8-52768f0b0764" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_a9088c78-1da7-48ba-aab8-d70d4eefa590" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingSensitivityDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementLoanServicingSensitivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingSensitivityDetails" xlink:type="extended" id="i68c93405d97b4580b3b0ad589661b3e3_FairValueMeasurementLoanServicingSensitivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_bb90cef2-b169-4b7d-8215-e201c7369ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_bb90cef2-b169-4b7d-8215-e201c7369ae9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_93c1df3d-5700-4a07-af6a-6d6374a94e4e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_93c1df3d-5700-4a07-af6a-6d6374a94e4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates_8c2b8bd7-48f6-48af-8855-952c4178ccc8" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:to="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates_8c2b8bd7-48f6-48af-8855-952c4178ccc8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates_382c30a0-522a-48c7-a5f3-eab7337bdb47" xlink:href="upst-20220630.xsd#upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:to="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates_382c30a0-522a-48c7-a5f3-eab7337bdb47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_716603e9-cbd6-4393-9587-079ce2c6ecc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_0572b0a4-725a-4597-b6cc-857e641c65db" xlink:to="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_716603e9-cbd6-4393-9587-079ce2c6ecc3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b4949d79-ffef-4a90-b859-054601c625ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_716603e9-cbd6-4393-9587-079ce2c6ecc3" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b4949d79-ffef-4a90-b859-054601c625ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b4949d79-ffef-4a90-b859-054601c625ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b4949d79-ffef-4a90-b859-054601c625ee" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b4949d79-ffef-4a90-b859-054601c625ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_79765089-9cef-4b51-8b61-00f6921ed308" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b4949d79-ffef-4a90-b859-054601c625ee" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_79765089-9cef-4b51-8b61-00f6921ed308" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_a2b91c5d-af89-4a59-a1db-08e52ec63829" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_79765089-9cef-4b51-8b61-00f6921ed308" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_a2b91c5d-af89-4a59-a1db-08e52ec63829" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_418f80dd-a54a-47a7-adb2-2695e4722d7f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_716603e9-cbd6-4393-9587-079ce2c6ecc3" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_418f80dd-a54a-47a7-adb2-2695e4722d7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_418f80dd-a54a-47a7-adb2-2695e4722d7f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_418f80dd-a54a-47a7-adb2-2695e4722d7f" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_418f80dd-a54a-47a7-adb2-2695e4722d7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ab3609a-0272-4c32-882a-3405700f8f59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_418f80dd-a54a-47a7-adb2-2695e4722d7f" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ab3609a-0272-4c32-882a-3405700f8f59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingAssetsMember_86d143b0-b7a4-4a37-8921-41a8baa89b4d" xlink:href="upst-20220630.xsd#upst_LoanServicingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9ab3609a-0272-4c32-882a-3405700f8f59" xlink:to="loc_upst_LoanServicingAssetsMember_86d143b0-b7a4-4a37-8921-41a8baa89b4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_ebddf464-3a8a-4730-9f59-3215d9c846de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_716603e9-cbd6-4393-9587-079ce2c6ecc3" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_ebddf464-3a8a-4730-9f59-3215d9c846de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_ebddf464-3a8a-4730-9f59-3215d9c846de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_ebddf464-3a8a-4730-9f59-3215d9c846de" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_ebddf464-3a8a-4730-9f59-3215d9c846de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de73e07b-1ed4-46e4-a0a6-24d87e839b52" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_ebddf464-3a8a-4730-9f59-3215d9c846de" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de73e07b-1ed4-46e4-a0a6-24d87e839b52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingLiabilitiesMember_5a9ddabe-7abc-4bf2-b0b1-3eb78617376c" xlink:href="upst-20220630.xsd#upst_LoanServicingLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de73e07b-1ed4-46e4-a0a6-24d87e839b52" xlink:to="loc_upst_LoanServicingLiabilitiesMember_5a9ddabe-7abc-4bf2-b0b1-3eb78617376c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingRollforwardDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementLoanServicingRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingRollforwardDetails" xlink:type="extended" id="i2976fc718d534342ba1521ab95509e08_FairValueMeasurementLoanServicingRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetsAtFairValueLineItems_20fc4da8-8d57-47f5-b9fb-59ebad4ae497" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAtFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_930f7151-1921-4d41-84e4-4cfd7ca3e2bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmountRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingAssetsAtFairValueLineItems_20fc4da8-8d57-47f5-b9fb-59ebad4ae497" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_930f7151-1921-4d41-84e4-4cfd7ca3e2bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_05448557-a11e-43c6-8d69-9048f503174c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_930f7151-1921-4d41-84e4-4cfd7ca3e2bd" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_05448557-a11e-43c6-8d69-9048f503174c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAdditions_851bf343-b7ac-409a-a342-d9d4003f3e61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_930f7151-1921-4d41-84e4-4cfd7ca3e2bd" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAdditions_851bf343-b7ac-409a-a342-d9d4003f3e61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingAssetAtFairValueGainLossIncludedInEarnings_4e091125-f5b9-4516-adbb-ebcccecc1b01" xlink:href="upst-20220630.xsd#upst_ServicingAssetAtFairValueGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_930f7151-1921-4d41-84e4-4cfd7ca3e2bd" xlink:to="loc_upst_ServicingAssetAtFairValueGainLossIncludedInEarnings_4e091125-f5b9-4516-adbb-ebcccecc1b01" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_dcc7fbbc-a398-4880-b7ca-19bb4bd16c29" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetsAtFairValueTable_2b757fd7-59e6-416a-9a2f-c5b8f8eaa043" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAtFairValueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ServicingAssetsAtFairValueLineItems_20fc4da8-8d57-47f5-b9fb-59ebad4ae497" xlink:to="loc_us-gaap_ServicingAssetsAtFairValueTable_2b757fd7-59e6-416a-9a2f-c5b8f8eaa043" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_022c7361-c9f2-4c43-8486-b0596f09f3ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ServicingAssetsAtFairValueTable_2b757fd7-59e6-416a-9a2f-c5b8f8eaa043" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_022c7361-c9f2-4c43-8486-b0596f09f3ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_022c7361-c9f2-4c43-8486-b0596f09f3ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_022c7361-c9f2-4c43-8486-b0596f09f3ee" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_022c7361-c9f2-4c43-8486-b0596f09f3ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8734c2a2-2e4d-4f3d-8919-2f2e6269906a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_022c7361-c9f2-4c43-8486-b0596f09f3ee" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8734c2a2-2e4d-4f3d-8919-2f2e6269906a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingAssetsMember_61f9dcff-7a9a-4755-b067-a54ce40c0798" xlink:href="upst-20220630.xsd#upst_LoanServicingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8734c2a2-2e4d-4f3d-8919-2f2e6269906a" xlink:to="loc_upst_LoanServicingAssetsMember_61f9dcff-7a9a-4755-b067-a54ce40c0798" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4a883814-7fa8-41d0-a377-aa0d9e163d86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ServicingAssetsAtFairValueTable_2b757fd7-59e6-416a-9a2f-c5b8f8eaa043" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4a883814-7fa8-41d0-a377-aa0d9e163d86" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4a883814-7fa8-41d0-a377-aa0d9e163d86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4a883814-7fa8-41d0-a377-aa0d9e163d86" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4a883814-7fa8-41d0-a377-aa0d9e163d86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_63a14dcf-60c0-4f29-a5a8-dc9cf1fb7c44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4a883814-7fa8-41d0-a377-aa0d9e163d86" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_63a14dcf-60c0-4f29-a5a8-dc9cf1fb7c44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_dc2e74ea-cc87-4623-8ca0-f1e554190a71" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_63a14dcf-60c0-4f29-a5a8-dc9cf1fb7c44" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_dc2e74ea-cc87-4623-8ca0-f1e554190a71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilitiesAtFairValueLineItems_2461e9d8-da02-4617-86a7-db7e1a5714b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilitiesAtFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_e13b83bb-fa43-4dd1-a6e5-f2506d078a8f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAmountRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingLiabilitiesAtFairValueLineItems_2461e9d8-da02-4617-86a7-db7e1a5714b5" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_e13b83bb-fa43-4dd1-a6e5-f2506d078a8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_5b04061d-e9ec-4a61-8b46-04e6b8bef4d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_e13b83bb-fa43-4dd1-a6e5-f2506d078a8f" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_5b04061d-e9ec-4a61-8b46-04e6b8bef4d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAdditions_18a1474f-fa85-47c4-aaab-18dbbc352ae2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_e13b83bb-fa43-4dd1-a6e5-f2506d078a8f" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAdditions_18a1474f-fa85-47c4-aaab-18dbbc352ae2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings_c42f5e8d-5472-4293-bb17-1214c30e0857" xlink:href="upst-20220630.xsd#upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_e13b83bb-fa43-4dd1-a6e5-f2506d078a8f" xlink:to="loc_upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings_c42f5e8d-5472-4293-bb17-1214c30e0857" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_aa3d8527-9dc7-461c-a0cb-971850d95aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilityAtFairValueAmount"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilitiesAtFairValueTable_d1897fa5-9f41-4024-9c46-c33b29978339" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingLiabilitiesAtFairValueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ServicingLiabilitiesAtFairValueLineItems_2461e9d8-da02-4617-86a7-db7e1a5714b5" xlink:to="loc_us-gaap_ServicingLiabilitiesAtFairValueTable_d1897fa5-9f41-4024-9c46-c33b29978339" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_81e53af8-0738-4b5a-940f-fce42a573038" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ServicingLiabilitiesAtFairValueTable_d1897fa5-9f41-4024-9c46-c33b29978339" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_81e53af8-0738-4b5a-940f-fce42a573038" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_81e53af8-0738-4b5a-940f-fce42a573038_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b9b78356-8257-4cb0-a5ed-2b4d3a84e614" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_43f3427a-4f01-47a7-80a8-de45b6ee2e30" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_5418c024-12a1-4663-a9dd-2af18154fd3f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ServicingLiabilitiesAtFairValueTable_d1897fa5-9f41-4024-9c46-c33b29978339" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_5418c024-12a1-4663-a9dd-2af18154fd3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_5418c024-12a1-4663-a9dd-2af18154fd3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_5418c024-12a1-4663-a9dd-2af18154fd3f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_5418c024-12a1-4663-a9dd-2af18154fd3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_d8f8b055-b469-4918-bd1a-7d46aab6e08e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_5418c024-12a1-4663-a9dd-2af18154fd3f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_d8f8b055-b469-4918-bd1a-7d46aab6e08e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingLiabilitiesMember_731bfb47-a520-451b-9dcd-db15a1fdc03c" xlink:href="upst-20220630.xsd#upst_LoanServicingLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_d8f8b055-b469-4918-bd1a-7d46aab6e08e" xlink:to="loc_upst_LoanServicingLiabilitiesMember_731bfb47-a520-451b-9dcd-db15a1fdc03c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementTrailingFeeRollforwardDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#FairValueMeasurementTrailingFeeRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementTrailingFeeRollforwardDetails" xlink:type="extended" id="i457359edf776455586b69b356e317acf_FairValueMeasurementTrailingFeeRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_5169ea9a-b2d7-4b32-87d3-a8f11f3715bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_5169ea9a-b2d7-4b32-87d3-a8f11f3715bb" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_6691a1f1-0ae5-4c5e-92ac-f86974393e8d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_6691a1f1-0ae5-4c5e-92ac-f86974393e8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_7fb2631b-2b76-4954-b835-ee874d4ba6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_7fb2631b-2b76-4954-b835-ee874d4ba6bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_a0227909-fd3c-4f8e-a452-a0b74d28dcd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_a0227909-fd3c-4f8e-a452-a0b74d28dcd2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_fd1c639e-7d9a-4c02-a0a6-26cce01ba76b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01e78065-c35c-492a-a4e7-3df945673a88" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_fd1c639e-7d9a-4c02-a0a6-26cce01ba76b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_e364a2bb-d117-47f3-9b3b-c9beff91e653" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef540b02-9009-47e7-bd04-a968b1bb870a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_5169ea9a-b2d7-4b32-87d3-a8f11f3715bb" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef540b02-9009-47e7-bd04-a968b1bb870a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_793202a1-7c36-4c14-9da4-82fb03fd61dd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef540b02-9009-47e7-bd04-a968b1bb870a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_793202a1-7c36-4c14-9da4-82fb03fd61dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_793202a1-7c36-4c14-9da4-82fb03fd61dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_793202a1-7c36-4c14-9da4-82fb03fd61dd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_793202a1-7c36-4c14-9da4-82fb03fd61dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ed68ec2d-ac11-42e6-9be9-287d06c14db3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_793202a1-7c36-4c14-9da4-82fb03fd61dd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ed68ec2d-ac11-42e6-9be9-287d06c14db3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_e1fc1377-b173-4851-a392-876ed956ccaf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ed68ec2d-ac11-42e6-9be9-287d06c14db3" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_e1fc1377-b173-4851-a392-876ed956ccaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_bd40efe5-d5cf-4895-988a-327ab41f0868" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef540b02-9009-47e7-bd04-a968b1bb870a" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_bd40efe5-d5cf-4895-988a-327ab41f0868" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_bd40efe5-d5cf-4895-988a-327ab41f0868_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_bd40efe5-d5cf-4895-988a-327ab41f0868" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_bd40efe5-d5cf-4895-988a-327ab41f0868_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_510b7fd7-c951-4d82-bf1f-a7ba1c1dedd3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_bd40efe5-d5cf-4895-988a-327ab41f0868" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_510b7fd7-c951-4d82-bf1f-a7ba1c1dedd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilitiesMember_36436288-fd39-4287-9e71-49e8705f0971" xlink:href="upst-20220630.xsd#upst_TrailingFeeLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_510b7fd7-c951-4d82-bf1f-a7ba1c1dedd3" xlink:to="loc_upst_TrailingFeeLiabilitiesMember_36436288-fd39-4287-9e71-49e8705f0971" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="extended" id="i83f447e839c34c2cb1ca8b92787e0f58_GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_e97b4f13-d735-4039-aaea-904575453a13" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_e97b4f13-d735-4039-aaea-904575453a13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_10cde08e-efc3-4087-b7e4-625b345bf5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_10cde08e-efc3-4087-b7e4-625b345bf5ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_32c52bb4-bb06-4bf0-a754-044a4bf98042" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_32c52bb4-bb06-4bf0-a754-044a4bf98042" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_1cf8a318-19c9-4381-9b02-d35e8bce1dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_1cf8a318-19c9-4381-9b02-d35e8bce1dc3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff282983-33a5-4502-b718-9d99320702d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_35c99921-88aa-4a5f-9d32-051aaa1d7dee" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff282983-33a5-4502-b718-9d99320702d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2a8212aa-ce6f-434c-804c-1003a8e91d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff282983-33a5-4502-b718-9d99320702d4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2a8212aa-ce6f-434c-804c-1003a8e91d4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2a8212aa-ce6f-434c-804c-1003a8e91d4c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2a8212aa-ce6f-434c-804c-1003a8e91d4c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2a8212aa-ce6f-434c-804c-1003a8e91d4c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_4ee05948-5bf9-4779-92d2-d90aa8936fcf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2a8212aa-ce6f-434c-804c-1003a8e91d4c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_4ee05948-5bf9-4779-92d2-d90aa8936fcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_a351d604-f4e6-42e9-9506-c59bfbbbde06" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_4ee05948-5bf9-4779-92d2-d90aa8936fcf" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_a351d604-f4e6-42e9-9506-c59bfbbbde06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_894d347d-9a08-4ade-811d-c2c8cf2c6d77" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_4ee05948-5bf9-4779-92d2-d90aa8936fcf" xlink:to="loc_us-gaap_CustomerRelationshipsMember_894d347d-9a08-4ade-811d-c2c8cf2c6d77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_69ec0066-9cee-451b-959e-9edce7538222" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff282983-33a5-4502-b718-9d99320702d4" xlink:to="loc_srt_RangeAxis_69ec0066-9cee-451b-959e-9edce7538222" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_69ec0066-9cee-451b-959e-9edce7538222_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_69ec0066-9cee-451b-959e-9edce7538222" xlink:to="loc_srt_RangeMember_69ec0066-9cee-451b-959e-9edce7538222_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_87652d3e-ddd4-4d18-a336-d8fe1d5c3b4b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_69ec0066-9cee-451b-959e-9edce7538222" xlink:to="loc_srt_RangeMember_87652d3e-ddd4-4d18-a336-d8fe1d5c3b4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_10e634cc-464b-4c78-ae42-e772b19233b4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_87652d3e-ddd4-4d18-a336-d8fe1d5c3b4b" xlink:to="loc_srt_WeightedAverageMember_10e634cc-464b-4c78-ae42-e772b19233b4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BalanceSheetComponentsPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#BalanceSheetComponentsPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BalanceSheetComponentsPropertyPlantandEquipmentDetails" xlink:type="extended" id="i1823457a3f054523ba9990c487f48cc5_BalanceSheetComponentsPropertyPlantandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_2f65fdc3-5fb0-46e0-9909-c10b451943fb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_2f65fdc3-5fb0-46e0-9909-c10b451943fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_34a7ab4d-235a-44f6-a095-94d4298fa50c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_34a7ab4d-235a-44f6-a095-94d4298fa50c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_e3dcef50-d977-4297-aba4-c2f1d6f15d17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_e3dcef50-d977-4297-aba4-c2f1d6f15d17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_f627c164-7f28-4a1d-991f-81ba4d91293f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_Depreciation_f627c164-7f28-4a1d-991f-81ba4d91293f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareNet_f4d75738-8cf2-4c62-af2d-cd0c95ef9ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalizedComputerSoftwareNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareNet_f4d75738-8cf2-4c62-af2d-cd0c95ef9ae7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7922f84d-e170-4c6b-a67d-c6fb153692cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_8cbc140c-f150-4370-8403-de097cfde722" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7922f84d-e170-4c6b-a67d-c6fb153692cb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_cd9b8522-f57d-40aa-b482-9ac6c8ff724c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7922f84d-e170-4c6b-a67d-c6fb153692cb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_cd9b8522-f57d-40aa-b482-9ac6c8ff724c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_cd9b8522-f57d-40aa-b482-9ac6c8ff724c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_cd9b8522-f57d-40aa-b482-9ac6c8ff724c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_cd9b8522-f57d-40aa-b482-9ac6c8ff724c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_cd9b8522-f57d-40aa-b482-9ac6c8ff724c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_8a55904b-6db2-4ef0-beaa-adc10d8a5d0c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_8a55904b-6db2-4ef0-beaa-adc10d8a5d0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_dcb6fb62-aa0b-49ac-9a77-3973582bb78e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:to="loc_us-gaap_ComputerEquipmentMember_dcb6fb62-aa0b-49ac-9a77-3973582bb78e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_e370bb10-0e8d-4cfc-a687-f4818ac8f1bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_e370bb10-0e8d-4cfc-a687-f4818ac8f1bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_a6b00baa-4682-4c63-9caf-eca3117ebb36" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f5660394-e21f-4651-b6f9-2b6e12a67d50" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_a6b00baa-4682-4c63-9caf-eca3117ebb36" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/AcquisitionsConsiderationTransferredDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#AcquisitionsConsiderationTransferredDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/AcquisitionsConsiderationTransferredDetails" xlink:type="extended" id="i6ceab216cf364bf5a5c1ce1efa4a090e_AcquisitionsConsiderationTransferredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_c8414d17-9094-49c1-b85a-b9eeabbf91d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_c8414d17-9094-49c1-b85a-b9eeabbf91d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_ce28b6cb-2bab-4a2a-a93b-c1b3010168c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_ce28b6cb-2bab-4a2a-a93b-c1b3010168c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BusinessCombinationConsiderationTransferredAssumedOptionsAttributableToPreCombinationServices_873321e0-4411-4804-a344-938b3735a5a3" xlink:href="upst-20220630.xsd#upst_BusinessCombinationConsiderationTransferredAssumedOptionsAttributableToPreCombinationServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_upst_BusinessCombinationConsiderationTransferredAssumedOptionsAttributableToPreCombinationServices_873321e0-4411-4804-a344-938b3735a5a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BusinessCombinationConsiderationTransferredTransactionCostPaidOnBehalfOfAcquire_7509a53c-67d3-41ba-89ab-48ea875abe55" xlink:href="upst-20220630.xsd#upst_BusinessCombinationConsiderationTransferredTransactionCostPaidOnBehalfOfAcquire"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_upst_BusinessCombinationConsiderationTransferredTransactionCostPaidOnBehalfOfAcquire_7509a53c-67d3-41ba-89ab-48ea875abe55" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_f751a53c-a512-4dbf-aabe-50c3925a86d7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_f751a53c-a512-4dbf-aabe-50c3925a86d7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShares_259b4c56-75e1-4894-866f-a7fc48ca44ab" xlink:href="upst-20220630.xsd#upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShares_259b4c56-75e1-4894-866f-a7fc48ca44ab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_cca1f20b-1b05-40e7-af5c-025c25a04f13" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_cca1f20b-1b05-40e7-af5c-025c25a04f13" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareHeldInEscrow_8f7e9415-ee34-479f-9c9a-587be994bd00" xlink:href="upst-20220630.xsd#upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareHeldInEscrow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_upst_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareHeldInEscrow_8f7e9415-ee34-479f-9c9a-587be994bd00" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EscrowDeposit_87b5d7f0-2f15-47ff-a725-4fe57ee33e9b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_EscrowDeposit_87b5d7f0-2f15-47ff-a725-4fe57ee33e9b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a3a8d2cc-fc98-4142-bcb7-778153581f17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b44a9bc3-268e-4ba7-ab7f-d4f47252b9e2" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a3a8d2cc-fc98-4142-bcb7-778153581f17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5895ac3c-7767-4b93-8c81-17149ff7ac8d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a3a8d2cc-fc98-4142-bcb7-778153581f17" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5895ac3c-7767-4b93-8c81-17149ff7ac8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5895ac3c-7767-4b93-8c81-17149ff7ac8d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5895ac3c-7767-4b93-8c81-17149ff7ac8d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5895ac3c-7767-4b93-8c81-17149ff7ac8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83a0500a-95de-41cc-a5a9-a78274eac6f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5895ac3c-7767-4b93-8c81-17149ff7ac8d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83a0500a-95de-41cc-a5a9-a78274eac6f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_69d8985f-7d28-4733-830b-de3d9a20558c" xlink:href="upst-20220630.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83a0500a-95de-41cc-a5a9-a78274eac6f3" xlink:to="loc_upst_ProdigySoftwareIncMember_69d8985f-7d28-4733-830b-de3d9a20558c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/AcquisitionsNarrativeDetails" xlink:type="extended" id="i71b67b323a224dc9875f518b4856fbb1_AcquisitionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_0ca42289-fd4f-44ee-bc62-bccd049add0a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_0ca42289-fd4f-44ee-bc62-bccd049add0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_bcfe9899-4156-4fb5-aa2b-270de9be49c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_bcfe9899-4156-4fb5-aa2b-270de9be49c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_d08c2151-6348-406a-909b-3eb46d55452f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_d08c2151-6348-406a-909b-3eb46d55452f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchaseOptionPercentage_023d9b9c-ab65-478e-b9a5-2a00b9c0858b" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchaseOptionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchaseOptionPercentage_023d9b9c-ab65-478e-b9a5-2a00b9c0858b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchasePeriod_5c78a857-d41d-4757-86ee-6779e34e2eb2" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardRepurchasePeriod_5c78a857-d41d-4757-86ee-6779e34e2eb2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpenseRecognitionPeriod_2a99420a-aa76-4690-a92d-ed3006d1cc32" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpenseRecognitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpenseRecognitionPeriod_2a99420a-aa76-4690-a92d-ed3006d1cc32" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_c268efd9-3f3e-4a9c-9872-fe615ddc0ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_c268efd9-3f3e-4a9c-9872-fe615ddc0ec2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_7a7e1af7-8b72-429a-a172-26387053ab77" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_7a7e1af7-8b72-429a-a172-26387053ab77" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_b0f2cf77-2fb8-473a-b16e-01a548762f55" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_b0f2cf77-2fb8-473a-b16e-01a548762f55" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e53e3de7-9a12-451b-9c96-c9fdcd950e63" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ad9e835-6743-431c-b053-f293b6324146" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e53e3de7-9a12-451b-9c96-c9fdcd950e63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_66d0bc24-930c-4b8e-ad3c-0537764b01e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e53e3de7-9a12-451b-9c96-c9fdcd950e63" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_66d0bc24-930c-4b8e-ad3c-0537764b01e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_66d0bc24-930c-4b8e-ad3c-0537764b01e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_66d0bc24-930c-4b8e-ad3c-0537764b01e3" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_66d0bc24-930c-4b8e-ad3c-0537764b01e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_18161d3d-caba-4f74-ba2e-fb6fffe38509" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_66d0bc24-930c-4b8e-ad3c-0537764b01e3" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_18161d3d-caba-4f74-ba2e-fb6fffe38509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_6d36e24d-d938-4bf1-a104-0bd98f36cdbb" xlink:href="upst-20220630.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_18161d3d-caba-4f74-ba2e-fb6fffe38509" xlink:to="loc_upst_ProdigySoftwareIncMember_6d36e24d-d938-4bf1-a104-0bd98f36cdbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f3c55730-d381-44a0-817c-d643f44a866d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e53e3de7-9a12-451b-9c96-c9fdcd950e63" xlink:to="loc_us-gaap_AwardTypeAxis_f3c55730-d381-44a0-817c-d643f44a866d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f3c55730-d381-44a0-817c-d643f44a866d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f3c55730-d381-44a0-817c-d643f44a866d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f3c55730-d381-44a0-817c-d643f44a866d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df29ae0-76e9-43f7-82e3-bc3e855a8ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f3c55730-d381-44a0-817c-d643f44a866d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df29ae0-76e9-43f7-82e3-bc3e855a8ab1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_72587622-4679-457a-8aa6-f721365feb21" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df29ae0-76e9-43f7-82e3-bc3e855a8ab1" xlink:to="loc_us-gaap_RestrictedStockMember_72587622-4679-457a-8aa6-f721365feb21" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/AcquisitionsPurchasePriceAllocationDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#AcquisitionsPurchasePriceAllocationDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/AcquisitionsPurchasePriceAllocationDetails" xlink:type="extended" id="i73e9f26192044ee486dcab1bee09150f_AcquisitionsPurchasePriceAllocationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_1a6868c6-bdf9-41d4-9128-a0df4150f5db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_Goodwill_1a6868c6-bdf9-41d4-9128-a0df4150f5db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_e7621d8d-81b5-43b6-a6ed-6b8460a014c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_e7621d8d-81b5-43b6-a6ed-6b8460a014c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_e3539c8a-b865-41e1-8236-1baf4e5aa5d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_e3539c8a-b865-41e1-8236-1baf4e5aa5d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_0eeca12d-e1d9-4992-8785-7ff4e76743c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_0eeca12d-e1d9-4992-8785-7ff4e76743c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssetsAcquiredLiabilitiesAssumedNet_a61892c2-f9f7-4956-8a0d-da5ea8d87512" xlink:href="upst-20220630.xsd#upst_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssetsAcquiredLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_upst_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssetsAcquiredLiabilitiesAssumedNet_a61892c2-f9f7-4956-8a0d-da5ea8d87512" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_39b949f2-b7c9-4e3c-b689-5118051b312d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_39b949f2-b7c9-4e3c-b689-5118051b312d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_90876a2b-f00e-416e-96c4-9294b3031ae4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_1a650838-d3d4-4448-8275-5781f0e95ba5" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_90876a2b-f00e-416e-96c4-9294b3031ae4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_41eeb346-66dd-467d-824a-73608e2d91a6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_90876a2b-f00e-416e-96c4-9294b3031ae4" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_41eeb346-66dd-467d-824a-73608e2d91a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_41eeb346-66dd-467d-824a-73608e2d91a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_41eeb346-66dd-467d-824a-73608e2d91a6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_41eeb346-66dd-467d-824a-73608e2d91a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_964c94d0-9cf0-464a-8247-b99cbefe781a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_41eeb346-66dd-467d-824a-73608e2d91a6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_964c94d0-9cf0-464a-8247-b99cbefe781a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_26e692a2-037e-4f83-a71c-d8161aee12f9" xlink:href="upst-20220630.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_964c94d0-9cf0-464a-8247-b99cbefe781a" xlink:to="loc_upst_ProdigySoftwareIncMember_26e692a2-037e-4f83-a71c-d8161aee12f9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/AcquisitionsIntangibleAssetsDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#AcquisitionsIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/AcquisitionsIntangibleAssetsDetails" xlink:type="extended" id="i651f9d12ed204fbf8a8459989d75047e_AcquisitionsIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_a1d41240-cf6d-4e46-9965-6a30cc0f4333" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b1ccc820-e78a-4608-b7bf-89dabbac8c85" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a1d41240-cf6d-4e46-9965-6a30cc0f4333" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b1ccc820-e78a-4608-b7bf-89dabbac8c85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_51b5ce3c-e16e-4356-ac65-d36186e0ad6f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a1d41240-cf6d-4e46-9965-6a30cc0f4333" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_51b5ce3c-e16e-4356-ac65-d36186e0ad6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e5369faa-cf4b-48c7-afa6-02a5f7d609b4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a1d41240-cf6d-4e46-9965-6a30cc0f4333" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e5369faa-cf4b-48c7-afa6-02a5f7d609b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_79015638-fd87-4537-b5c0-b66a51e08799" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e5369faa-cf4b-48c7-afa6-02a5f7d609b4" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_79015638-fd87-4537-b5c0-b66a51e08799" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_79015638-fd87-4537-b5c0-b66a51e08799_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_79015638-fd87-4537-b5c0-b66a51e08799" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_79015638-fd87-4537-b5c0-b66a51e08799_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_51f84d28-e8f9-4846-9e19-632f4cc050b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_79015638-fd87-4537-b5c0-b66a51e08799" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_51f84d28-e8f9-4846-9e19-632f4cc050b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_036a76d4-8c1b-4cb6-b377-3cfc065fe5ce" xlink:href="upst-20220630.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_51f84d28-e8f9-4846-9e19-632f4cc050b6" xlink:to="loc_upst_ProdigySoftwareIncMember_036a76d4-8c1b-4cb6-b377-3cfc065fe5ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_27f3c2a5-3ed1-45ab-900d-e08752c63fd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e5369faa-cf4b-48c7-afa6-02a5f7d609b4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_27f3c2a5-3ed1-45ab-900d-e08752c63fd2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_27f3c2a5-3ed1-45ab-900d-e08752c63fd2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_27f3c2a5-3ed1-45ab-900d-e08752c63fd2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_27f3c2a5-3ed1-45ab-900d-e08752c63fd2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bd04c832-63f4-471f-8175-43a4bab675d6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_27f3c2a5-3ed1-45ab-900d-e08752c63fd2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bd04c832-63f4-471f-8175-43a4bab675d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_f991c2b3-63ba-45ce-b828-b23c6f1e1346" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bd04c832-63f4-471f-8175-43a4bab675d6" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_f991c2b3-63ba-45ce-b828-b23c6f1e1346" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_eed12d4c-886f-4ac9-8698-93cc7fd732ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bd04c832-63f4-471f-8175-43a4bab675d6" xlink:to="loc_us-gaap_TradeNamesMember_eed12d4c-886f-4ac9-8698-93cc7fd732ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_6ef4ef8d-fae6-453c-853b-99de90fd34bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bd04c832-63f4-471f-8175-43a4bab675d6" xlink:to="loc_us-gaap_CustomerRelationshipsMember_6ef4ef8d-fae6-453c-853b-99de90fd34bf" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsSummaryDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#BorrowingsSummaryDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsSummaryDetails" xlink:type="extended" id="i0592a1cc325642a5b531aea4566ebf80_BorrowingsSummaryDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_bde267f4-10a4-44a5-8181-d9f15d14cfea" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LongTermAndShortTermDebtGross_433abb3d-c2f8-42b3-a57e-139bca88a2e0" xlink:href="upst-20220630.xsd#upst_LongTermAndShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_bde267f4-10a4-44a5-8181-d9f15d14cfea" xlink:to="loc_upst_LongTermAndShortTermDebtGross_433abb3d-c2f8-42b3-a57e-139bca88a2e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_6f93b5ad-d2a0-495c-9667-71c4269e99f7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_bde267f4-10a4-44a5-8181-d9f15d14cfea" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_6f93b5ad-d2a0-495c-9667-71c4269e99f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_d3d27e0e-0566-483f-a2c2-9ff3ee0aa4f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_bde267f4-10a4-44a5-8181-d9f15d14cfea" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_d3d27e0e-0566-483f-a2c2-9ff3ee0aa4f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_f4dd2485-d5b3-42e2-afff-ae58af42ecd8" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_bde267f4-10a4-44a5-8181-d9f15d14cfea" xlink:to="loc_upst_ScheduleOfBorrowingsTable_f4dd2485-d5b3-42e2-afff-ae58af42ecd8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_2868315a-0935-419c-89be-84f94fd3436c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_f4dd2485-d5b3-42e2-afff-ae58af42ecd8" xlink:to="loc_us-gaap_DebtInstrumentAxis_2868315a-0935-419c-89be-84f94fd3436c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2868315a-0935-419c-89be-84f94fd3436c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_2868315a-0935-419c-89be-84f94fd3436c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2868315a-0935-419c-89be-84f94fd3436c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a0614fc9-b8e3-4bdd-8fb1-d8905879a9c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_2868315a-0935-419c-89be-84f94fd3436c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a0614fc9-b8e3-4bdd-8fb1-d8905879a9c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_WarehouseCreditFacilityMember_0e8981e1-ebf1-4e9b-80a9-c9f135f455e0" xlink:href="upst-20220630.xsd#upst_WarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_a0614fc9-b8e3-4bdd-8fb1-d8905879a9c6" xlink:to="loc_upst_WarehouseCreditFacilityMember_0e8981e1-ebf1-4e9b-80a9-c9f135f455e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_RiskRetentionFundingLoansMember_db72cba3-1d9f-443a-87fe-867bfa85ca47" xlink:href="upst-20220630.xsd#upst_RiskRetentionFundingLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_a0614fc9-b8e3-4bdd-8fb1-d8905879a9c6" xlink:to="loc_upst_RiskRetentionFundingLoansMember_db72cba3-1d9f-443a-87fe-867bfa85ca47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TwentyTwentySixNotesMember_cdf08012-bb84-4186-aa7b-b6c364f5f4d0" xlink:href="upst-20220630.xsd#upst_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_a0614fc9-b8e3-4bdd-8fb1-d8905879a9c6" xlink:to="loc_upst_TwentyTwentySixNotesMember_cdf08012-bb84-4186-aa7b-b6c364f5f4d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_eed1a68b-3ff9-4585-a139-ec4b134b1040" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_f4dd2485-d5b3-42e2-afff-ae58af42ecd8" xlink:to="loc_us-gaap_CreditFacilityAxis_eed1a68b-3ff9-4585-a139-ec4b134b1040" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_eed1a68b-3ff9-4585-a139-ec4b134b1040_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_eed1a68b-3ff9-4585-a139-ec4b134b1040" xlink:to="loc_us-gaap_CreditFacilityDomain_eed1a68b-3ff9-4585-a139-ec4b134b1040_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_92fadba9-adcc-4bd6-81cc-98887d8fdd08" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_eed1a68b-3ff9-4585-a139-ec4b134b1040" xlink:to="loc_us-gaap_CreditFacilityDomain_92fadba9-adcc-4bd6-81cc-98887d8fdd08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_f7a686cb-22d7-4f43-9f7d-a887448acca6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_92fadba9-adcc-4bd6-81cc-98887d8fdd08" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_f7a686cb-22d7-4f43-9f7d-a887448acca6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#BorrowingsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsNarrativeDetails" xlink:type="extended" id="i654112ebc1634a258dab6582301fd18a_BorrowingsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_93300b7f-d6bc-487c-b677-ae2d36db7c71" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_93300b7f-d6bc-487c-b677-ae2d36db7c71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_9440166f-af71-493f-a809-ee0028b4b036" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_9440166f-af71-493f-a809-ee0028b4b036" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_25c5c421-d86b-489d-aee8-722f07d3dad5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_25c5c421-d86b-489d-aee8-722f07d3dad5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_a54b857f-6e4b-40b6-ab94-0e9cf5717b4f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_a54b857f-6e4b-40b6-ab94-0e9cf5717b4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LineOfCreditFacilityMaximumAdvanceRate_7d5dca07-fff9-4272-9e36-6ae593750fe3" xlink:href="upst-20220630.xsd#upst_LineOfCreditFacilityMaximumAdvanceRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_LineOfCreditFacilityMaximumAdvanceRate_7d5dca07-fff9-4272-9e36-6ae593750fe3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LongTermAndShortTermDebtGross_090d1ee2-d0c0-4267-b15a-dba97368ff30" xlink:href="upst-20220630.xsd#upst_LongTermAndShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_LongTermAndShortTermDebtGross_090d1ee2-d0c0-4267-b15a-dba97368ff30" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_8d03c220-ebef-4c40-9b78-866175c3e8f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_8d03c220-ebef-4c40-9b78-866175c3e8f3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_600ea08c-1760-48f5-b558-38857ac01262" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_600ea08c-1760-48f5-b558-38857ac01262" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentAdditionalAggregatePrincipal_468c0267-8cfe-4945-967e-5798f61c2c35" xlink:href="upst-20220630.xsd#upst_DebtInstrumentAdditionalAggregatePrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_DebtInstrumentAdditionalAggregatePrincipal_468c0267-8cfe-4945-967e-5798f61c2c35" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_555c5938-9b3e-47f7-8e99-fe4252fec01f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_555c5938-9b3e-47f7-8e99-fe4252fec01f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_19949071-5653-4d25-99e1-c11dfd1dfc17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_19949071-5653-4d25-99e1-c11dfd1dfc17" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayable_e39a564d-856e-414a-bf3d-49a5b3fb72ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_ConvertibleNotesPayable_e39a564d-856e-414a-bf3d-49a5b3fb72ae" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_4157c85f-f2dc-455d-a9ae-bc1cc11c91d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_4157c85f-f2dc-455d-a9ae-bc1cc11c91d4" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_8bd49e41-77a4-4092-919b-a903fbb37165" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_8bd49e41-77a4-4092-919b-a903fbb37165" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_14dcec72-16e6-4321-bb4c-32b8666cec9f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_14dcec72-16e6-4321-bb4c-32b8666cec9f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_2d766d8b-7ec4-4d7c-b3a3-406a63e8fc33" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_2d766d8b-7ec4-4d7c-b3a3-406a63e8fc33" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e1be12b0-390b-44e2-97ed-71dd6f9bdaf4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e1be12b0-390b-44e2-97ed-71dd6f9bdaf4" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_15fa00fc-7dcf-48d9-8c8f-aac516be8674" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_15fa00fc-7dcf-48d9-8c8f-aac516be8674" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate_ed78a81f-ab79-4977-93d4-d5093b92290e" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate_ed78a81f-ab79-4977-93d4-d5093b92290e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_f67e17d9-ffea-439e-b1cc-7cd090db10c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_f67e17d9-ffea-439e-b1cc-7cd090db10c2" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_72a12006-5203-4c9d-8c14-c26ec43f7212" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_72a12006-5203-4c9d-8c14-c26ec43f7212" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_6e3c4728-43c0-431c-96c7-e888f8e09e4d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_6e3c4728-43c0-431c-96c7-e888f8e09e4d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5bf8264d-7f27-494d-bc6e-9f451973aac5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5bf8264d-7f27-494d-bc6e-9f451973aac5" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PaymentsForCappedCalls_d91092e3-4113-4834-841a-6aaacb3da77d" xlink:href="upst-20220630.xsd#upst_PaymentsForCappedCalls"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_PaymentsForCappedCalls_d91092e3-4113-4834-841a-6aaacb3da77d" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice_2fb4e110-3635-4098-80c9-72edb46c0956" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice_2fb4e110-3635-4098-80c9-72edb46c0956" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice_a58c9f33-35a8-4b27-ab09-f622001a2535" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice_a58c9f33-35a8-4b27-ab09-f622001a2535" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered_38c3d857-ecc0-4b98-8a64-b55e6704fae7" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered_38c3d857-ecc0-4b98-8a64-b55e6704fae7" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_95555d14-8ba6-49ce-8c47-992cdc0de816" xlink:to="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_e90b26f7-9b75-451e-a147-cd3ea229c1dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_us-gaap_VariableRateAxis_e90b26f7-9b75-451e-a147-cd3ea229c1dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_e90b26f7-9b75-451e-a147-cd3ea229c1dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_e90b26f7-9b75-451e-a147-cd3ea229c1dc" xlink:to="loc_us-gaap_VariableRateDomain_e90b26f7-9b75-451e-a147-cd3ea229c1dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_905f91d4-7db8-43b6-add5-8774c7bcb1d9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_e90b26f7-9b75-451e-a147-cd3ea229c1dc" xlink:to="loc_us-gaap_VariableRateDomain_905f91d4-7db8-43b6-add5-8774c7bcb1d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_c154c3be-7e01-43b4-b26e-2a6df82ab8bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_905f91d4-7db8-43b6-add5-8774c7bcb1d9" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_c154c3be-7e01-43b4-b26e-2a6df82ab8bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember_2e41c320-840d-47bb-8e45-310005d92078" xlink:href="upst-20220630.xsd#upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_905f91d4-7db8-43b6-add5-8774c7bcb1d9" xlink:to="loc_upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember_2e41c320-840d-47bb-8e45-310005d92078" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_05f86da5-2404-42ad-a9fa-3cd28a92fdb4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_us-gaap_DebtInstrumentAxis_05f86da5-2404-42ad-a9fa-3cd28a92fdb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_05f86da5-2404-42ad-a9fa-3cd28a92fdb4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_05f86da5-2404-42ad-a9fa-3cd28a92fdb4" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_05f86da5-2404-42ad-a9fa-3cd28a92fdb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b47bfe6e-7aba-476e-aebb-fecd2df383a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_05f86da5-2404-42ad-a9fa-3cd28a92fdb4" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b47bfe6e-7aba-476e-aebb-fecd2df383a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityMember_99442b1d-130e-419b-a8cd-22c8e38eb028" xlink:href="upst-20220630.xsd#upst_ULTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b47bfe6e-7aba-476e-aebb-fecd2df383a9" xlink:to="loc_upst_ULTWarehouseCreditFacilityMember_99442b1d-130e-419b-a8cd-22c8e38eb028" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityCommittedMember_c7e4f989-f359-49aa-a4c0-4bcc4fc19176" xlink:href="upst-20220630.xsd#upst_ULTWarehouseCreditFacilityCommittedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ULTWarehouseCreditFacilityMember_99442b1d-130e-419b-a8cd-22c8e38eb028" xlink:to="loc_upst_ULTWarehouseCreditFacilityCommittedMember_c7e4f989-f359-49aa-a4c0-4bcc4fc19176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityUncommittedMember_234cbdd8-d623-4998-9e90-bffd0eb1722e" xlink:href="upst-20220630.xsd#upst_ULTWarehouseCreditFacilityUncommittedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ULTWarehouseCreditFacilityMember_99442b1d-130e-419b-a8cd-22c8e38eb028" xlink:to="loc_upst_ULTWarehouseCreditFacilityUncommittedMember_234cbdd8-d623-4998-9e90-bffd0eb1722e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTWarehouseCreditFacilityMember_a33969ac-8b99-4561-a9d2-2dfe6e4f75eb" xlink:href="upst-20220630.xsd#upst_UAWTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b47bfe6e-7aba-476e-aebb-fecd2df383a9" xlink:to="loc_upst_UAWTWarehouseCreditFacilityMember_a33969ac-8b99-4561-a9d2-2dfe6e4f75eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TwentyTwentySixNotesMember_ec9265b8-c932-4da5-abf1-08530d132705" xlink:href="upst-20220630.xsd#upst_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b47bfe6e-7aba-476e-aebb-fecd2df383a9" xlink:to="loc_upst_TwentyTwentySixNotesMember_ec9265b8-c932-4da5-abf1-08530d132705" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_cafc1f15-9c0e-44ea-a403-f64d141196aa" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_srt_RangeAxis_cafc1f15-9c0e-44ea-a403-f64d141196aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_cafc1f15-9c0e-44ea-a403-f64d141196aa_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_cafc1f15-9c0e-44ea-a403-f64d141196aa" xlink:to="loc_srt_RangeMember_cafc1f15-9c0e-44ea-a403-f64d141196aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7d3fb3e2-0990-4ba0-861b-ca5ad1be88d4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_cafc1f15-9c0e-44ea-a403-f64d141196aa" xlink:to="loc_srt_RangeMember_7d3fb3e2-0990-4ba0-861b-ca5ad1be88d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_40654ccd-eafd-4d4b-a30d-5275a538041e" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7d3fb3e2-0990-4ba0-861b-ca5ad1be88d4" xlink:to="loc_srt_MinimumMember_40654ccd-eafd-4d4b-a30d-5275a538041e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_7a6b6d66-f167-450d-bb8d-51f97bec486c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7d3fb3e2-0990-4ba0-861b-ca5ad1be88d4" xlink:to="loc_srt_MaximumMember_7a6b6d66-f167-450d-bb8d-51f97bec486c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_5c348ac7-783c-4137-9e3f-499a296362f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_us-gaap_CreditFacilityAxis_5c348ac7-783c-4137-9e3f-499a296362f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5c348ac7-783c-4137-9e3f-499a296362f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_5c348ac7-783c-4137-9e3f-499a296362f4" xlink:to="loc_us-gaap_CreditFacilityDomain_5c348ac7-783c-4137-9e3f-499a296362f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_6d015368-0a90-4d32-829d-f5e92031c18b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_5c348ac7-783c-4137-9e3f-499a296362f4" xlink:to="loc_us-gaap_CreditFacilityDomain_6d015368-0a90-4d32-829d-f5e92031c18b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_70319c67-f248-414d-b250-92499a553963" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_6d015368-0a90-4d32-829d-f5e92031c18b" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_70319c67-f248-414d-b250-92499a553963" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_90d7844a-050b-4ebe-b6ec-3a2ed922947b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_90d7844a-050b-4ebe-b6ec-3a2ed922947b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_90d7844a-050b-4ebe-b6ec-3a2ed922947b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90d7844a-050b-4ebe-b6ec-3a2ed922947b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_90d7844a-050b-4ebe-b6ec-3a2ed922947b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b12a6eff-dbe7-44da-9ac5-b3ec47dc7e6a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_90d7844a-050b-4ebe-b6ec-3a2ed922947b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b12a6eff-dbe7-44da-9ac5-b3ec47dc7e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_a12faa0b-6386-40e4-9421-60473678eb6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_b12a6eff-dbe7-44da-9ac5-b3ec47dc7e6a" xlink:to="loc_us-gaap_ConvertibleDebtMember_a12faa0b-6386-40e4-9421-60473678eb6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionAxis_b4e47b91-0bd4-4eaf-a549-c91f7577092b" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConversionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_upst_DebtInstrumentConversionAxis_b4e47b91-0bd4-4eaf-a549-c91f7577092b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionDomain_b4e47b91-0bd4-4eaf-a549-c91f7577092b_default" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_upst_DebtInstrumentConversionAxis_b4e47b91-0bd4-4eaf-a549-c91f7577092b" xlink:to="loc_upst_DebtInstrumentConversionDomain_b4e47b91-0bd4-4eaf-a549-c91f7577092b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionDomain_74ca156a-df74-483e-a550-91bba59ec805" xlink:href="upst-20220630.xsd#upst_DebtInstrumentConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_upst_DebtInstrumentConversionAxis_b4e47b91-0bd4-4eaf-a549-c91f7577092b" xlink:to="loc_upst_DebtInstrumentConversionDomain_74ca156a-df74-483e-a550-91bba59ec805" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodOneMember_30abba0d-7a41-44c3-8fc2-5af44a58cfa1" xlink:href="upst-20220630.xsd#upst_ConversionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_74ca156a-df74-483e-a550-91bba59ec805" xlink:to="loc_upst_ConversionPeriodOneMember_30abba0d-7a41-44c3-8fc2-5af44a58cfa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodTwoMember_7910b68f-736b-4443-9f61-ac644e33124c" xlink:href="upst-20220630.xsd#upst_ConversionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_74ca156a-df74-483e-a550-91bba59ec805" xlink:to="loc_upst_ConversionPeriodTwoMember_7910b68f-736b-4443-9f61-ac644e33124c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodThreeMember_de6e5dd5-6031-43d7-af83-0fe92edce52d" xlink:href="upst-20220630.xsd#upst_ConversionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_74ca156a-df74-483e-a550-91bba59ec805" xlink:to="loc_upst_ConversionPeriodThreeMember_de6e5dd5-6031-43d7-af83-0fe92edce52d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ca675a4c-e279-4844-96e9-c4b3bfa4071c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ca675a4c-e279-4844-96e9-c4b3bfa4071c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ca675a4c-e279-4844-96e9-c4b3bfa4071c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ca675a4c-e279-4844-96e9-c4b3bfa4071c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ca675a4c-e279-4844-96e9-c4b3bfa4071c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2977045f-4f81-4335-bf4d-9e548cffde86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ca675a4c-e279-4844-96e9-c4b3bfa4071c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2977045f-4f81-4335-bf4d-9e548cffde86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_471a285d-2e00-4788-a3af-c7430551020a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2977045f-4f81-4335-bf4d-9e548cffde86" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_471a285d-2e00-4788-a3af-c7430551020a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_06197b71-967f-4999-b32a-37885dbe73bb" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_796c8db4-57bf-4249-a431-151e809acc88" xlink:to="loc_srt_ConsolidatedEntitiesAxis_06197b71-967f-4999-b32a-37885dbe73bb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_06197b71-967f-4999-b32a-37885dbe73bb_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_06197b71-967f-4999-b32a-37885dbe73bb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_06197b71-967f-4999-b32a-37885dbe73bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_e797982e-c142-4652-bb7f-b7658165272f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_06197b71-967f-4999-b32a-37885dbe73bb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_e797982e-c142-4652-bb7f-b7658165272f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PrimaryBeneficiaryMember_3fbdbeb8-611a-4625-8070-cb1bc7052d95" xlink:href="upst-20220630.xsd#upst_PrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_e797982e-c142-4652-bb7f-b7658165272f" xlink:to="loc_upst_PrimaryBeneficiaryMember_3fbdbeb8-611a-4625-8070-cb1bc7052d95" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsAssetsPledgedasCollateralDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#BorrowingsAssetsPledgedasCollateralDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsAssetsPledgedasCollateralDetails" xlink:type="extended" id="ie91c493a8d8042d9bba1f712363478c3_BorrowingsAssetsPledgedasCollateralDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LongTermAndShortTermDebtGross_c074cfdd-03aa-412a-8ed4-020bc0916763" xlink:href="upst-20220630.xsd#upst_LongTermAndShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:to="loc_upst_LongTermAndShortTermDebtGross_c074cfdd-03aa-412a-8ed4-020bc0916763" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_43881b9a-b2be-40ae-9652-101d3e60e23b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesReceivableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:to="loc_us-gaap_NotesReceivableGross_43881b9a-b2be-40ae-9652-101d3e60e23b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_aff4002c-2417-4597-bd50-f0cb2af6f4a7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_aff4002c-2417-4597-bd50-f0cb2af6f4a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_738c76e3-e971-4acd-964e-0e4af0ee6137" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:to="loc_us-gaap_RestrictedCash_738c76e3-e971-4acd-964e-0e4af0ee6137" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:href="upst-20220630.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_e597dea9-3940-498c-bb19-54069968de8b" xlink:to="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_0b56e2b7-b975-49b9-a9a2-9466309f7ac3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:to="loc_us-gaap_DebtInstrumentAxis_0b56e2b7-b975-49b9-a9a2-9466309f7ac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_0b56e2b7-b975-49b9-a9a2-9466309f7ac3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_0b56e2b7-b975-49b9-a9a2-9466309f7ac3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_0b56e2b7-b975-49b9-a9a2-9466309f7ac3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_fe3ef439-859b-4b1f-94c7-2aa626684144" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_0b56e2b7-b975-49b9-a9a2-9466309f7ac3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_fe3ef439-859b-4b1f-94c7-2aa626684144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityMember_8dcea01c-dc27-4ad5-b453-f1e9ec781351" xlink:href="upst-20220630.xsd#upst_ULTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_fe3ef439-859b-4b1f-94c7-2aa626684144" xlink:to="loc_upst_ULTWarehouseCreditFacilityMember_8dcea01c-dc27-4ad5-b453-f1e9ec781351" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTWarehouseCreditFacilityMember_88acbfa5-cc97-47d5-ae3f-f2a583337146" xlink:href="upst-20220630.xsd#upst_UAWTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_fe3ef439-859b-4b1f-94c7-2aa626684144" xlink:to="loc_upst_UAWTWarehouseCreditFacilityMember_88acbfa5-cc97-47d5-ae3f-f2a583337146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_5e733987-a869-4685-905b-cda65b1a4457" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:to="loc_us-gaap_CreditFacilityAxis_5e733987-a869-4685-905b-cda65b1a4457" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5e733987-a869-4685-905b-cda65b1a4457_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_5e733987-a869-4685-905b-cda65b1a4457" xlink:to="loc_us-gaap_CreditFacilityDomain_5e733987-a869-4685-905b-cda65b1a4457_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_bf4e9c06-6968-4d4a-b418-8f0a8bf5ea07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_5e733987-a869-4685-905b-cda65b1a4457" xlink:to="loc_us-gaap_CreditFacilityDomain_bf4e9c06-6968-4d4a-b418-8f0a8bf5ea07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_2a636c50-acee-4d42-bdf7-15c818f81876" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_bf4e9c06-6968-4d4a-b418-8f0a8bf5ea07" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_2a636c50-acee-4d42-bdf7-15c818f81876" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_77e1fad3-0829-4489-aa52-6a3bac87a418" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:to="loc_srt_ConsolidatedEntitiesAxis_77e1fad3-0829-4489-aa52-6a3bac87a418" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_77e1fad3-0829-4489-aa52-6a3bac87a418_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_77e1fad3-0829-4489-aa52-6a3bac87a418" xlink:to="loc_srt_ConsolidatedEntitiesDomain_77e1fad3-0829-4489-aa52-6a3bac87a418_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_4fd4df13-a877-4fdb-bdb0-1541feeced89" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_77e1fad3-0829-4489-aa52-6a3bac87a418" xlink:to="loc_srt_ConsolidatedEntitiesDomain_4fd4df13-a877-4fdb-bdb0-1541feeced89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_e1911ef6-a723-4b41-af09-0d2e23e54dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_4fd4df13-a877-4fdb-bdb0-1541feeced89" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_e1911ef6-a723-4b41-af09-0d2e23e54dc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusAxis_18887b85-f1ad-4a71-b693-d738dfabd154" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_b223b61f-f1a7-4520-b9c9-a81a40aaaaaa" xlink:to="loc_us-gaap_PledgedStatusAxis_18887b85-f1ad-4a71-b693-d738dfabd154" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_18887b85-f1ad-4a71-b693-d738dfabd154_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PledgedStatusAxis_18887b85-f1ad-4a71-b693-d738dfabd154" xlink:to="loc_us-gaap_PledgedStatusDomain_18887b85-f1ad-4a71-b693-d738dfabd154_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_a82cda50-e79f-41c4-bfa2-43859e19ec71" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PledgedStatusAxis_18887b85-f1ad-4a71-b693-d738dfabd154" xlink:to="loc_us-gaap_PledgedStatusDomain_a82cda50-e79f-41c4-bfa2-43859e19ec71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetPledgedAsCollateralMember_2be98f82-3bfe-4a2e-adb9-9c8b00542e65" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetPledgedAsCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PledgedStatusDomain_a82cda50-e79f-41c4-bfa2-43859e19ec71" xlink:to="loc_us-gaap_AssetPledgedAsCollateralMember_2be98f82-3bfe-4a2e-adb9-9c8b00542e65" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityReservedSharesofCommonStockforIssuanceDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityReservedSharesofCommonStockforIssuanceDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityReservedSharesofCommonStockforIssuanceDetails" xlink:type="extended" id="i2da216953a624ab5b4c5c0b674669bb5_StockholdersEquityReservedSharesofCommonStockforIssuanceDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_8641855e-3fa0-4612-b090-b1400864f91d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_7b237eb3-80f7-458a-86de-0c88739b1c15" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_8641855e-3fa0-4612-b090-b1400864f91d" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_7b237eb3-80f7-458a-86de-0c88739b1c15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_9d24c899-d0a6-4ff2-aa04-23b1c39ddcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_8641855e-3fa0-4612-b090-b1400864f91d" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_9d24c899-d0a6-4ff2-aa04-23b1c39ddcc2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_9d24c899-d0a6-4ff2-aa04-23b1c39ddcc2" xlink:to="loc_us-gaap_AwardTypeAxis_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4ca4b937-c2cf-4cd0-87f8-52b5f84d3cac" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7fc9beb9-b2a0-4ae4-9ce1-2f899d9c1a95" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7fc9beb9-b2a0-4ae4-9ce1-2f899d9c1a95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c84425cb-e179-4206-a3c5-b5ac34befe9c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c84425cb-e179-4206-a3c5-b5ac34befe9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_2cefe370-9226-4fe0-a98b-754a613e76b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:to="loc_us-gaap_PerformanceSharesMember_2cefe370-9226-4fe0-a98b-754a613e76b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_58623592-0318-48e4-ab4a-2bdbd1bab64b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b113d163-9538-42b1-81b7-ae10f2cba895" xlink:to="loc_us-gaap_EmployeeStockMember_58623592-0318-48e4-ab4a-2bdbd1bab64b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_b30aeef3-1613-4ce8-aafb-7b6f89abb722" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_9d24c899-d0a6-4ff2-aa04-23b1c39ddcc2" xlink:to="loc_us-gaap_PlanNameAxis_b30aeef3-1613-4ce8-aafb-7b6f89abb722" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_b30aeef3-1613-4ce8-aafb-7b6f89abb722_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_b30aeef3-1613-4ce8-aafb-7b6f89abb722" xlink:to="loc_us-gaap_PlanNameDomain_b30aeef3-1613-4ce8-aafb-7b6f89abb722_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_5872a06c-4908-4a67-b792-5faae37c4734" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_b30aeef3-1613-4ce8-aafb-7b6f89abb722" xlink:to="loc_us-gaap_PlanNameDomain_5872a06c-4908-4a67-b792-5faae37c4734" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_A2020EquityIncentivePlanMember_cf0c294a-0ccd-43d1-a1a3-25222c8bf62c" xlink:href="upst-20220630.xsd#upst_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5872a06c-4908-4a67-b792-5faae37c4734" xlink:to="loc_upst_A2020EquityIncentivePlanMember_cf0c294a-0ccd-43d1-a1a3-25222c8bf62c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1c642bf8-bbaf-4a68-8733-39996aba3138" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_9d24c899-d0a6-4ff2-aa04-23b1c39ddcc2" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1c642bf8-bbaf-4a68-8733-39996aba3138" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1c642bf8-bbaf-4a68-8733-39996aba3138_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1c642bf8-bbaf-4a68-8733-39996aba3138" xlink:to="loc_us-gaap_ClassOfStockDomain_1c642bf8-bbaf-4a68-8733-39996aba3138_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_832db2a0-5d1b-4a4b-8ea5-ad9e5fe2cd2f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1c642bf8-bbaf-4a68-8733-39996aba3138" xlink:to="loc_us-gaap_ClassOfStockDomain_832db2a0-5d1b-4a4b-8ea5-ad9e5fe2cd2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_a90786a3-4720-4f98-93aa-6fa4696238ff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_832db2a0-5d1b-4a4b-8ea5-ad9e5fe2cd2f" xlink:to="loc_us-gaap_CommonClassAMember_a90786a3-4720-4f98-93aa-6fa4696238ff" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityNarrativeDetails" xlink:type="extended" id="ia440b118932643eb8599d064c6534cc3_StockholdersEquityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_e443e7c8-8e7b-48d6-9b9d-be9012583821" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_e443e7c8-8e7b-48d6-9b9d-be9012583821" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_bd3739da-7a11-40e6-9a6f-560e288c3470" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_bd3739da-7a11-40e6-9a6f-560e288c3470" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_5358507e-f2c1-4617-953e-9cbe3b729aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_5358507e-f2c1-4617-953e-9cbe3b729aeb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_042ff919-d0ad-42a9-801c-3bc325b8fc1e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_042ff919-d0ad-42a9-801c-3bc325b8fc1e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_af922879-882b-44d7-af34-8ee26865ec07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_af922879-882b-44d7-af34-8ee26865ec07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_f948c580-08bd-4190-a078-f8fe8a569a7e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_f948c580-08bd-4190-a078-f8fe8a569a7e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_e8cfde6d-0a6f-40f1-b69f-823fc37b417d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_e8cfde6d-0a6f-40f1-b69f-823fc37b417d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_295bc700-f593-4e69-9351-bfe93197c823" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_295bc700-f593-4e69-9351-bfe93197c823" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_85201893-78d4-4518-9641-6e17e89510f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_85201893-78d4-4518-9641-6e17e89510f2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInAcquisitionWeightedAverageGrantDateFairValue_a53807ab-35cd-4d9a-b7ba-c06be3d129dd" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInAcquisitionWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAssumedInAcquisitionWeightedAverageGrantDateFairValue_a53807ab-35cd-4d9a-b7ba-c06be3d129dd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_89b4dce8-5310-4611-8c78-e14be552f067" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_89b4dce8-5310-4611-8c78-e14be552f067" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_010f6d20-8fda-4ad8-876b-cc2fe41aa913" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_010f6d20-8fda-4ad8-876b-cc2fe41aa913" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_5cbcf9fe-d94f-419b-a6b9-70b738a7fb88" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_5cbcf9fe-d94f-419b-a6b9-70b738a7fb88" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_b86be279-30c1-4d1f-84a4-33dc5523a9bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_b86be279-30c1-4d1f-84a4-33dc5523a9bd" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e136bda5-2398-4696-8734-e9f756741ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e136bda5-2398-4696-8734-e9f756741ea5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_bee05464-1f1d-41ba-8258-33e161c9590f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_bee05464-1f1d-41ba-8258-33e161c9590f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_8da16723-c0b5-4983-b6a7-678ab30ef7ce" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_8da16723-c0b5-4983-b6a7-678ab30ef7ce" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_2a7c6640-332c-493f-ae50-ee3652d3e6b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_2a7c6640-332c-493f-ae50-ee3652d3e6b7" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsPerformanceMeasurementAverageStockPriceConsecutiveTradingDays_317751fd-f65f-4770-ba4a-732ef6a928db" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsPerformanceMeasurementAverageStockPriceConsecutiveTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsPerformanceMeasurementAverageStockPriceConsecutiveTradingDays_317751fd-f65f-4770-ba4a-732ef6a928db" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_1478e24a-3d43-4ae9-bd6e-76b8fe18e714" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_1478e24a-3d43-4ae9-bd6e-76b8fe18e714" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_1787d216-28b3-40dc-bb1c-a09011ad45d5" xlink:href="upst-20220630.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_1787d216-28b3-40dc-bb1c-a09011ad45d5" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_17cc1190-c04c-4c69-a63c-14561a44af39" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_17cc1190-c04c-4c69-a63c-14561a44af39" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_8dd764ff-eea0-4f11-8f55-e1dc660fb7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_8dd764ff-eea0-4f11-8f55-e1dc660fb7c5" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5da7ccf0-0a6c-4195-9586-d65437329ad4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_8e49a31e-ae0e-4744-9291-db3fed91ddb6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_AwardTypeAxis_8e49a31e-ae0e-4744-9291-db3fed91ddb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8e49a31e-ae0e-4744-9291-db3fed91ddb6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8e49a31e-ae0e-4744-9291-db3fed91ddb6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8e49a31e-ae0e-4744-9291-db3fed91ddb6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8e49a31e-ae0e-4744-9291-db3fed91ddb6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5c1ae40e-b91e-450a-a1b7-9c8090e72c27" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5c1ae40e-b91e-450a-a1b7-9c8090e72c27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_217073aa-3ba1-49b3-bbf9-607d879b4792" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_217073aa-3ba1-49b3-bbf9-607d879b4792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_c2eb03f9-bfce-4625-bede-69b29f8a9051" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:to="loc_us-gaap_RestrictedStockMember_c2eb03f9-bfce-4625-bede-69b29f8a9051" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_ec4e23a9-ff47-46d6-b7c5-9992dad60ee5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:to="loc_us-gaap_PerformanceSharesMember_ec4e23a9-ff47-46d6-b7c5-9992dad60ee5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_2c833649-9666-4310-9506-f03489c4ede0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fb6aafb9-2436-4823-9e84-25821fa5606b" xlink:to="loc_us-gaap_EmployeeStockMember_2c833649-9666-4310-9506-f03489c4ede0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_28bfd7ab-0b37-4603-8d80-7316677e6271" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_PlanNameAxis_28bfd7ab-0b37-4603-8d80-7316677e6271" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_28bfd7ab-0b37-4603-8d80-7316677e6271_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_28bfd7ab-0b37-4603-8d80-7316677e6271" xlink:to="loc_us-gaap_PlanNameDomain_28bfd7ab-0b37-4603-8d80-7316677e6271_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_10523355-48da-45bc-b7b4-2ab8d6b9b9fc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_28bfd7ab-0b37-4603-8d80-7316677e6271" xlink:to="loc_us-gaap_PlanNameDomain_10523355-48da-45bc-b7b4-2ab8d6b9b9fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_A2020EquityIncentivePlanMember_9d9a22d9-5b38-49f5-b71c-ae3d80fae58b" xlink:href="upst-20220630.xsd#upst_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_10523355-48da-45bc-b7b4-2ab8d6b9b9fc" xlink:to="loc_upst_A2020EquityIncentivePlanMember_9d9a22d9-5b38-49f5-b71c-ae3d80fae58b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_50c37f7c-924a-4ba9-b4ce-15e60c4733ec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_StatementClassOfStockAxis_50c37f7c-924a-4ba9-b4ce-15e60c4733ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_50c37f7c-924a-4ba9-b4ce-15e60c4733ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_50c37f7c-924a-4ba9-b4ce-15e60c4733ec" xlink:to="loc_us-gaap_ClassOfStockDomain_50c37f7c-924a-4ba9-b4ce-15e60c4733ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6e87e38f-aae3-4201-b878-ca495c42e188" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_50c37f7c-924a-4ba9-b4ce-15e60c4733ec" xlink:to="loc_us-gaap_ClassOfStockDomain_6e87e38f-aae3-4201-b878-ca495c42e188" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_0c41c1ba-970b-4f41-b1f3-0066d2cd1c33" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6e87e38f-aae3-4201-b878-ca495c42e188" xlink:to="loc_us-gaap_CommonClassAMember_0c41c1ba-970b-4f41-b1f3-0066d2cd1c33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1270d24c-b572-44d1-9ba7-7362b707f9c0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_srt_RangeAxis_1270d24c-b572-44d1-9ba7-7362b707f9c0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1270d24c-b572-44d1-9ba7-7362b707f9c0_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1270d24c-b572-44d1-9ba7-7362b707f9c0" xlink:to="loc_srt_RangeMember_1270d24c-b572-44d1-9ba7-7362b707f9c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_dd7db3f9-4aba-4785-a70c-b57e3506e3ae" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1270d24c-b572-44d1-9ba7-7362b707f9c0" xlink:to="loc_srt_RangeMember_dd7db3f9-4aba-4785-a70c-b57e3506e3ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_93719f2f-9bb9-4a79-824d-c0fff804a239" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_dd7db3f9-4aba-4785-a70c-b57e3506e3ae" xlink:to="loc_srt_MinimumMember_93719f2f-9bb9-4a79-824d-c0fff804a239" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fdee35d4-07ff-4793-8658-338a1a447fc8" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_dd7db3f9-4aba-4785-a70c-b57e3506e3ae" xlink:to="loc_srt_MaximumMember_fdee35d4-07ff-4793-8658-338a1a447fc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_f789ca35-a0a0-450e-9865-d418f4042845" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_dd7db3f9-4aba-4785-a70c-b57e3506e3ae" xlink:to="loc_srt_WeightedAverageMember_f789ca35-a0a0-450e-9865-d418f4042845" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_8d1308aa-5bae-4063-9351-160dcb42f1bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_ValuationTechniqueAxis_8d1308aa-5bae-4063-9351-160dcb42f1bd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_8d1308aa-5bae-4063-9351-160dcb42f1bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_8d1308aa-5bae-4063-9351-160dcb42f1bd" xlink:to="loc_us-gaap_ValuationTechniqueDomain_8d1308aa-5bae-4063-9351-160dcb42f1bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_42ff151f-f5f3-4594-825f-a50b06d55608" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_8d1308aa-5bae-4063-9351-160dcb42f1bd" xlink:to="loc_us-gaap_ValuationTechniqueDomain_42ff151f-f5f3-4594-825f-a50b06d55608" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BlackScholesOptionPricingModelMember_6f9bd647-47ff-4e40-b4fb-25acc15d994c" xlink:href="upst-20220630.xsd#upst_BlackScholesOptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_42ff151f-f5f3-4594-825f-a50b06d55608" xlink:to="loc_upst_BlackScholesOptionPricingModelMember_6f9bd647-47ff-4e40-b4fb-25acc15d994c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_82e63f14-3b58-4496-9f98-1d8cc1741763" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_82e63f14-3b58-4496-9f98-1d8cc1741763" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_82e63f14-3b58-4496-9f98-1d8cc1741763_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_82e63f14-3b58-4496-9f98-1d8cc1741763" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_82e63f14-3b58-4496-9f98-1d8cc1741763_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_eea73a71-8fa1-45ee-aaff-a788dfdd4584" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_82e63f14-3b58-4496-9f98-1d8cc1741763" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_eea73a71-8fa1-45ee-aaff-a788dfdd4584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_71a0fe64-c9a8-420e-93f4-2b20ad7a24ca" xlink:href="upst-20220630.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_eea73a71-8fa1-45ee-aaff-a788dfdd4584" xlink:to="loc_upst_ProdigySoftwareIncMember_71a0fe64-c9a8-420e-93f4-2b20ad7a24ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_62c3397b-2c96-40a3-a60c-314f8b665f06" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_VestingAxis_62c3397b-2c96-40a3-a60c-314f8b665f06" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_62c3397b-2c96-40a3-a60c-314f8b665f06_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_62c3397b-2c96-40a3-a60c-314f8b665f06" xlink:to="loc_us-gaap_VestingDomain_62c3397b-2c96-40a3-a60c-314f8b665f06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_4e1a6e68-b4dd-4c0a-92d4-7a4e72f4b6bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_62c3397b-2c96-40a3-a60c-314f8b665f06" xlink:to="loc_us-gaap_VestingDomain_4e1a6e68-b4dd-4c0a-92d4-7a4e72f4b6bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_784e9b72-5537-4717-b785-596d88059321" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e1a6e68-b4dd-4c0a-92d4-7a4e72f4b6bb" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_784e9b72-5537-4717-b785-596d88059321" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_b2f62358-bdcd-444a-9298-8aba2cfa7023" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e1a6e68-b4dd-4c0a-92d4-7a4e72f4b6bb" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_b2f62358-bdcd-444a-9298-8aba2cfa7023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_645f1f45-1a42-4d84-9e5b-10f616242c94" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a80cbbd9-e56f-4508-bfa0-7c588ef4b4ac" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_645f1f45-1a42-4d84-9e5b-10f616242c94" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_645f1f45-1a42-4d84-9e5b-10f616242c94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_645f1f45-1a42-4d84-9e5b-10f616242c94" xlink:to="loc_us-gaap_EquityComponentDomain_645f1f45-1a42-4d84-9e5b-10f616242c94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f927c0ac-06aa-4994-83d5-e2a46c8bc637" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_645f1f45-1a42-4d84-9e5b-10f616242c94" xlink:to="loc_us-gaap_EquityComponentDomain_f927c0ac-06aa-4994-83d5-e2a46c8bc637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_f9b54f32-e6b7-47d7-9b9d-838bb544c089" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f927c0ac-06aa-4994-83d5-e2a46c8bc637" xlink:to="loc_us-gaap_CommonStockMember_f9b54f32-e6b7-47d7-9b9d-838bb544c089" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityRSUActivityDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityRSUActivityDetails" xlink:type="extended" id="i4bbc7a62ad8d4bfb86c9675de2fd19bc_StockholdersEquityRSUActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_efb421c6-8e5f-49e0-afe5-98f9e9a1a395" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_efb421c6-8e5f-49e0-afe5-98f9e9a1a395" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2a8bc62b-18c6-4e25-9ffe-58f791bccc16" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2a8bc62b-18c6-4e25-9ffe-58f791bccc16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01e15716-104f-4809-b52d-037454f3ddf1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01e15716-104f-4809-b52d-037454f3ddf1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_2b15039b-bb45-4426-99b8-4a1d4180dcc1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_2b15039b-bb45-4426-99b8-4a1d4180dcc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_d02629a0-45eb-49ff-8508-0d395ed0ad94" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_a465a987-ac68-493d-a1e2-fc79fa6c82c0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_d02629a0-45eb-49ff-8508-0d395ed0ad94" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_d387e52b-6a2a-4241-8b6f-53706f9eb98c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_efb421c6-8e5f-49e0-afe5-98f9e9a1a395" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_4f0bec71-514b-4bbe-a4cd-8c5e30f6ba5c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_4f0bec71-514b-4bbe-a4cd-8c5e30f6ba5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d5802209-630a-42e8-ba67-7bb31629e789" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d5802209-630a-42e8-ba67-7bb31629e789" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_e62895f2-d214-4a37-83d4-d9436a9979b9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_e62895f2-d214-4a37-83d4-d9436a9979b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_58316adc-038f-42ce-8e56-89a882c1604f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_5304fa1a-2708-481e-9623-c8e1071fb68a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_58316adc-038f-42ce-8e56-89a882c1604f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2f94f54d-1507-47ba-8363-c645f74ff80b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_efb421c6-8e5f-49e0-afe5-98f9e9a1a395" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2f94f54d-1507-47ba-8363-c645f74ff80b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2f94f54d-1507-47ba-8363-c645f74ff80b" xlink:to="loc_us-gaap_AwardTypeAxis_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7c7d388-6194-4a53-808f-949fe6d2d2d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b2f0bacf-ee8f-4805-8e36-80f6c59aefd2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7c7d388-6194-4a53-808f-949fe6d2d2d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_ae364c43-0190-4fe6-a938-934810b436b0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7c7d388-6194-4a53-808f-949fe6d2d2d8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_ae364c43-0190-4fe6-a938-934810b436b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_87953888-e44b-41bc-bd2a-cc15a9789315" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7c7d388-6194-4a53-808f-949fe6d2d2d8" xlink:to="loc_us-gaap_RestrictedStockMember_87953888-e44b-41bc-bd2a-cc15a9789315" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityRestrictedStockActivityDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityRestrictedStockActivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityRestrictedStockActivityDetails" xlink:type="extended" id="ib1de838b2b3a42bbb51eebe9bc22bd6b_StockholdersEquityRestrictedStockActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b660c49e-a275-4207-bbef-f5fb85b12660" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_584a6bf0-8e16-40a1-aab7-6f4a9f41c851" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b660c49e-a275-4207-bbef-f5fb85b12660" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_584a6bf0-8e16-40a1-aab7-6f4a9f41c851" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_45cc8b8c-b12b-45dd-81ce-2fc14187f74d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_584a6bf0-8e16-40a1-aab7-6f4a9f41c851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_45cc8b8c-b12b-45dd-81ce-2fc14187f74d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_00e6ccb3-8a61-4815-80a3-c279a083b416" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_584a6bf0-8e16-40a1-aab7-6f4a9f41c851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_00e6ccb3-8a61-4815-80a3-c279a083b416" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c63bc79b-8c76-47ed-b249-6f3fe8f16775" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0a17ec0c-a7f7-4bb3-9245-ac5d92cd69c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b660c49e-a275-4207-bbef-f5fb85b12660" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0a17ec0c-a7f7-4bb3-9245-ac5d92cd69c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5666273d-07f6-447a-861f-4e646f459fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0a17ec0c-a7f7-4bb3-9245-ac5d92cd69c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5666273d-07f6-447a-861f-4e646f459fd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_576d6b4c-3e8d-4ab3-8d76-4cd8231eeb87" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_0a17ec0c-a7f7-4bb3-9245-ac5d92cd69c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_576d6b4c-3e8d-4ab3-8d76-4cd8231eeb87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50ec2ff8-bf9e-40f6-bcea-20d49ac26766" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b660c49e-a275-4207-bbef-f5fb85b12660" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50ec2ff8-bf9e-40f6-bcea-20d49ac26766" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50ec2ff8-bf9e-40f6-bcea-20d49ac26766" xlink:to="loc_us-gaap_AwardTypeAxis_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ce57b97b-b673-45c5-b066-5daeb5bc9676" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c8ec8941-ef9b-4eac-810a-8f23ecfaa7f9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ce57b97b-b673-45c5-b066-5daeb5bc9676" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_789818c8-efc6-4e83-9451-b1448c290732" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ce57b97b-b673-45c5-b066-5daeb5bc9676" xlink:to="loc_us-gaap_RestrictedStockMember_789818c8-efc6-4e83-9451-b1448c290732" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityWeightedAverageAssumptionsDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityWeightedAverageAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityWeightedAverageAssumptionsDetails" xlink:type="extended" id="i6c5be8bff9b94fd08eef8f883bfb8e4c_StockholdersEquityWeightedAverageAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_ecbc1364-2fca-4af6-9891-65c31932fbfd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_ecbc1364-2fca-4af6-9891-65c31932fbfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_39125cb9-db23-4d2e-8d67-6463ce57a9e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_39125cb9-db23-4d2e-8d67-6463ce57a9e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_bf620423-48ad-4ec4-bd80-c306dc09e627" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_bf620423-48ad-4ec4-bd80-c306dc09e627" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_24f034b5-ad2a-430e-99d5-3deb71041f11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_24f034b5-ad2a-430e-99d5-3deb71041f11" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_fe67bc9e-e0c3-41ab-b85a-f8aaa1023aff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_fe67bc9e-e0c3-41ab-b85a-f8aaa1023aff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e3fc83fc-d5b8-4b92-b6aa-d359116c7da8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e3fc83fc-d5b8-4b92-b6aa-d359116c7da8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_1347addd-a6fc-40af-9305-f2bafeca79a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_1347addd-a6fc-40af-9305-f2bafeca79a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_ccebf38a-df7e-44db-9354-9df06d259966" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_ccebf38a-df7e-44db-9354-9df06d259966" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_11b6f9ed-9742-4fdf-a24a-9fa595b59bec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_11b6f9ed-9742-4fdf-a24a-9fa595b59bec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b51b80f1-2eee-4f9a-8f9f-1d024b3b50bc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9257eacb-999c-4f70-94d9-fdbc47694eae" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b51b80f1-2eee-4f9a-8f9f-1d024b3b50bc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_3ba682b9-7441-4823-a6f9-323c10d56119" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b51b80f1-2eee-4f9a-8f9f-1d024b3b50bc" xlink:to="loc_us-gaap_AwardTypeAxis_3ba682b9-7441-4823-a6f9-323c10d56119" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ba682b9-7441-4823-a6f9-323c10d56119_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_3ba682b9-7441-4823-a6f9-323c10d56119" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ba682b9-7441-4823-a6f9-323c10d56119_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08895f44-d98e-4c19-90f6-b8dd0757e89c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_3ba682b9-7441-4823-a6f9-323c10d56119" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08895f44-d98e-4c19-90f6-b8dd0757e89c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5f2504d5-1ac8-4549-afca-b4e6280c5df3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08895f44-d98e-4c19-90f6-b8dd0757e89c" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5f2504d5-1ac8-4549-afca-b4e6280c5df3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_4c3bcb43-ae90-40b8-aa75-0e8aa5cf2664" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08895f44-d98e-4c19-90f6-b8dd0757e89c" xlink:to="loc_us-gaap_PerformanceSharesMember_4c3bcb43-ae90-40b8-aa75-0e8aa5cf2664" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_e55b8e19-768e-41c8-9ff7-955b22f17001" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08895f44-d98e-4c19-90f6-b8dd0757e89c" xlink:to="loc_us-gaap_EmployeeStockMember_e55b8e19-768e-41c8-9ff7-955b22f17001" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01766816-47f0-4691-a680-3a6e7f138590" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b51b80f1-2eee-4f9a-8f9f-1d024b3b50bc" xlink:to="loc_srt_RangeAxis_01766816-47f0-4691-a680-3a6e7f138590" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01766816-47f0-4691-a680-3a6e7f138590_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01766816-47f0-4691-a680-3a6e7f138590" xlink:to="loc_srt_RangeMember_01766816-47f0-4691-a680-3a6e7f138590_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f2efadb5-ff45-4832-9934-ee5f254b11de" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01766816-47f0-4691-a680-3a6e7f138590" xlink:to="loc_srt_RangeMember_f2efadb5-ff45-4832-9934-ee5f254b11de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01e1f000-a269-4ca2-b895-4a1f94535a0f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f2efadb5-ff45-4832-9934-ee5f254b11de" xlink:to="loc_srt_MinimumMember_01e1f000-a269-4ca2-b895-4a1f94535a0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_12a04797-0407-4abf-9753-fef6de6d2525" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f2efadb5-ff45-4832-9934-ee5f254b11de" xlink:to="loc_srt_MaximumMember_12a04797-0407-4abf-9753-fef6de6d2525" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityExpenseDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#StockholdersEquityExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityExpenseDetails" xlink:type="extended" id="i142ae813bdbb4c6db44d777cac02536d_StockholdersEquityExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7d021f45-a556-4ee5-9583-583f220b759e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_7e542231-b914-482d-9297-620fed6b5469" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7d021f45-a556-4ee5-9583-583f220b759e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_7e542231-b914-482d-9297-620fed6b5469" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_9f0f95b1-b3c0-46db-bdf4-3a9d7adca8ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7d021f45-a556-4ee5-9583-583f220b759e" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_9f0f95b1-b3c0-46db-bdf4-3a9d7adca8ae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_8afc22af-8dab-4dee-a6a3-0536b549e37f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_9f0f95b1-b3c0-46db-bdf4-3a9d7adca8ae" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_8afc22af-8dab-4dee-a6a3-0536b549e37f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8afc22af-8dab-4dee-a6a3-0536b549e37f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8afc22af-8dab-4dee-a6a3-0536b549e37f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8afc22af-8dab-4dee-a6a3-0536b549e37f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8afc22af-8dab-4dee-a6a3-0536b549e37f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_d0647960-131b-4685-87e5-d67b8abcd404" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_d0647960-131b-4685-87e5-d67b8abcd404" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerOperationsMember_4132875c-d14f-47e5-b0e0-fc3dbfb2bfe9" xlink:href="upst-20220630.xsd#upst_CustomerOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:to="loc_upst_CustomerOperationsMember_4132875c-d14f-47e5-b0e0-fc3dbfb2bfe9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_EngineeringAndProductDevelopmentMember_eacf18f3-5d5d-436a-af1a-6077d4db8edb" xlink:href="upst-20220630.xsd#upst_EngineeringAndProductDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:to="loc_upst_EngineeringAndProductDevelopmentMember_eacf18f3-5d5d-436a-af1a-6077d4db8edb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_82fe3cf0-434d-45c5-a1a6-84ea680bd56f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_2991ea18-dbe8-465e-9de1-5d7fb19fa2b5" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_82fe3cf0-434d-45c5-a1a6-84ea680bd56f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/CommitmentandContingenciesDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#CommitmentandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CommitmentandContingenciesDetails" xlink:type="extended" id="i20a9177683e04cc2a00e51dbd107ace3_CommitmentandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_b035f6c0-e742-40c9-9f4e-7ce755871dc8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligation_39b25372-bd89-4ac0-96a9-f37a39a5b463" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b035f6c0-e742-40c9-9f4e-7ce755871dc8" xlink:to="loc_us-gaap_PurchaseObligation_39b25372-bd89-4ac0-96a9-f37a39a5b463" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_0dfcde1c-61fd-47ec-95b7-5e92f81b14d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b035f6c0-e742-40c9-9f4e-7ce755871dc8" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_0dfcde1c-61fd-47ec-95b7-5e92f81b14d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_82906f1c-0455-473d-bf3e-881acedcc6ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_b035f6c0-e742-40c9-9f4e-7ce755871dc8" xlink:to="loc_us-gaap_LossContingenciesTable_82906f1c-0455-473d-bf3e-881acedcc6ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_60a4445b-eae5-48e2-ab8a-afcbc3147b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_82906f1c-0455-473d-bf3e-881acedcc6ed" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_60a4445b-eae5-48e2-ab8a-afcbc3147b2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_60a4445b-eae5-48e2-ab8a-afcbc3147b2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_60a4445b-eae5-48e2-ab8a-afcbc3147b2e" xlink:to="loc_us-gaap_LossContingencyNatureDomain_60a4445b-eae5-48e2-ab8a-afcbc3147b2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_2cf78ce2-1006-4861-a27a-5f434d016803" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_60a4445b-eae5-48e2-ab8a-afcbc3147b2e" xlink:to="loc_us-gaap_LossContingencyNatureDomain_2cf78ce2-1006-4861-a27a-5f434d016803" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ObligationToRepurchaseReceivablesSoldMember_f1fdd263-c6b9-42e6-af46-e7998b960848" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ObligationToRepurchaseReceivablesSoldMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_2cf78ce2-1006-4861-a27a-5f434d016803" xlink:to="loc_us-gaap_ObligationToRepurchaseReceivablesSoldMember_f1fdd263-c6b9-42e6-af46-e7998b960848" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/NetIncomeLossPerShareAntidilutiveSecuritiesDetails" xlink:type="simple" xlink:href="upst-20220630.xsd#NetIncomeLossPerShareAntidilutiveSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/NetIncomeLossPerShareAntidilutiveSecuritiesDetails" xlink:type="extended" id="i7d7f607e58514dd791d803c4ff0c4fb9_NetIncomeLossPerShareAntidilutiveSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f9e64dcc-e985-4c0f-ba4b-bed15bcb79ab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_185b9fe8-6303-45f8-abf0-996f009f8b32" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f9e64dcc-e985-4c0f-ba4b-bed15bcb79ab" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_185b9fe8-6303-45f8-abf0-996f009f8b32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2e0ec6ba-e113-4c0b-ac6d-adfc82cafbd5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f9e64dcc-e985-4c0f-ba4b-bed15bcb79ab" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2e0ec6ba-e113-4c0b-ac6d-adfc82cafbd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ecdf019e-a1e7-46f8-bc0b-f027031936bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2e0ec6ba-e113-4c0b-ac6d-adfc82cafbd5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ecdf019e-a1e7-46f8-bc0b-f027031936bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ecdf019e-a1e7-46f8-bc0b-f027031936bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ecdf019e-a1e7-46f8-bc0b-f027031936bd" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ecdf019e-a1e7-46f8-bc0b-f027031936bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ecdf019e-a1e7-46f8-bc0b-f027031936bd" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_b0fb1955-1ed0-42b4-b177-feddbbcca8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_b0fb1955-1ed0-42b4-b177-feddbbcca8dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_bb538275-fe5f-4b48-afd9-e90b5cd9bf71" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_bb538275-fe5f-4b48-afd9-e90b5cd9bf71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PerformanceRestrictedStockUnitsPRSUsMember_933114f9-3ccb-462b-9a35-ab49a217977f" xlink:href="upst-20220630.xsd#upst_PerformanceRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:to="loc_upst_PerformanceRestrictedStockUnitsPRSUsMember_933114f9-3ccb-462b-9a35-ab49a217977f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_3db22c07-f4a1-46ec-9372-2e4b24c740c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:to="loc_us-gaap_EmployeeStockMember_3db22c07-f4a1-46ec-9372-2e4b24c740c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_493ffac7-140a-43aa-9fc2-95ba04f4b6f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9285fccc-1b49-4a7c-b87b-0b9f1cec274b" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_493ffac7-140a-43aa-9fc2-95ba04f4b6f8" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
