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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:10e31bee-f5d8-4282-a3a0-d4ef4038d94a,g:cac7de97-f08d-4923-85cc-4a79fbe5149e-->
<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-20230331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="i88122524feea44689f33af324d68e034_CondensedConsolidatedBalanceSheetsParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01ab8052-7f87-4827-8f10-3046561ec591" 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_13ec7e70-1af5-48b0-bfac-c254f63bbfbb" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_OtherAssetsFairValueDisclosure_13ec7e70-1af5-48b0-bfac-c254f63bbfbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure_131d6979-703a-42f3-92e2-8536a2ac1441" xlink:href="upst-20230331.xsd#upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_upst_AccruedExpensesAndOtherLiabilitiesFairValueDisclosure_131d6979-703a-42f3-92e2-8536a2ac1441" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_f4fe511f-4552-4417-b162-bd93b3d2007a" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_f4fe511f-4552-4417-b162-bd93b3d2007a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_444fba0a-47e1-4172-9e2b-8432f6d8078c" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_444fba0a-47e1-4172-9e2b-8432f6d8078c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_ce26493c-6d7e-4ec7-9374-bf0a23c0d3d0" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_CommonStockSharesIssued_ce26493c-6d7e-4ec7-9374-bf0a23c0d3d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f5821f8b-a274-4b48-89c1-9d93a0ff57ba" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f5821f8b-a274-4b48-89c1-9d93a0ff57ba" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_b4d3b6be-1888-4065-a6a9-83dad5cede09" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityDisclosuresAbstract_b4d3b6be-1888-4065-a6a9-83dad5cede09" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_398905da-f54a-46e3-ad95-3f4b08c8f5e8" 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_b4d3b6be-1888-4065-a6a9-83dad5cede09" xlink:to="loc_us-gaap_AssetsAbstract_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_5ca15fe8-caeb-4d73-b95d-91e2b9234250" 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_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:to="loc_us-gaap_Cash_5ca15fe8-caeb-4d73-b95d-91e2b9234250" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_f16755e3-6147-448f-bec6-2ee35ecf4434" 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_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:to="loc_us-gaap_RestrictedCash_f16755e3-6147-448f-bec6-2ee35ecf4434" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_c0562428-5c74-4a2f-9dcc-28a1f72a95e1" 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_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:to="loc_us-gaap_NotesReceivableNet_c0562428-5c74-4a2f-9dcc-28a1f72a95e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_10e7ec8c-0575-4f49-8412-fa704b742a0a" 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_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:to="loc_us-gaap_OtherAssets_10e7ec8c-0575-4f49-8412-fa704b742a0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_5323e462-5d4b-43e9-b9d9-04aa409fec19" 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_398905da-f54a-46e3-ad95-3f4b08c8f5e8" xlink:to="loc_us-gaap_Assets_5323e462-5d4b-43e9-b9d9-04aa409fec19" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsFairValueDisclosure_b5a54bce-8668-4c8e-9139-106b859d324b" 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_e32cac98-86e3-4ed1-9769-f2e3b64d954e" 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_b4d3b6be-1888-4065-a6a9-83dad5cede09" xlink:to="loc_us-gaap_LiabilitiesAbstract_e32cac98-86e3-4ed1-9769-f2e3b64d954e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_2742949a-e73f-48f8-98c1-8db61e5cd610" 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_e32cac98-86e3-4ed1-9769-f2e3b64d954e" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_2742949a-e73f-48f8-98c1-8db61e5cd610" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_45c36c88-f6c8-43c4-9894-253d99e5505c" 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_e32cac98-86e3-4ed1-9769-f2e3b64d954e" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_45c36c88-f6c8-43c4-9894-253d99e5505c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_59510a18-9b5b-40ea-b8df-14a9c957c9d9" 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_e32cac98-86e3-4ed1-9769-f2e3b64d954e" xlink:to="loc_us-gaap_Liabilities_59510a18-9b5b-40ea-b8df-14a9c957c9d9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_c82bc9ec-1f8a-431b-9ed0-a21958492db3" 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_e32cac98-86e3-4ed1-9769-f2e3b64d954e" xlink:to="loc_us-gaap_StockholdersEquity_c82bc9ec-1f8a-431b-9ed0-a21958492db3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_36da4675-5fbc-425c-ac8c-b369bc50969a" 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_01ab8052-7f87-4827-8f10-3046561ec591" xlink:to="loc_us-gaap_StatementTable_36da4675-5fbc-425c-ac8c-b369bc50969a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_9d7e9888-0850-421a-9984-9e92c53ec306" 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_36da4675-5fbc-425c-ac8c-b369bc50969a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_9d7e9888-0850-421a-9984-9e92c53ec306" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_9d7e9888-0850-421a-9984-9e92c53ec306_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_9d7e9888-0850-421a-9984-9e92c53ec306" xlink:to="loc_srt_ConsolidatedEntitiesDomain_9d7e9888-0850-421a-9984-9e92c53ec306_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_d0175595-0b4d-479d-abb0-567b97b777eb" 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_9d7e9888-0850-421a-9984-9e92c53ec306" xlink:to="loc_srt_ConsolidatedEntitiesDomain_d0175595-0b4d-479d-abb0-567b97b777eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_d54979c2-855c-4b6c-8306-3834517650cb" 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_d0175595-0b4d-479d-abb0-567b97b777eb" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_d54979c2-855c-4b6c-8306-3834517650cb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="upst-20230331.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended" id="ie85a32d9521c4b7ebf3e2a4b80ef85e3_CondensedConsolidatedStatementsofStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_51c2758b-acb2-4bd7-8501-f5b2801e62b1" 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_552ce567-3c43-4e89-acdf-89a44d900979" 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_51c2758b-acb2-4bd7-8501-f5b2801e62b1" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_552ce567-3c43-4e89-acdf-89a44d900979" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f89df657-db40-4881-b34f-21e4f72f5fa7" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f89df657-db40-4881-b34f-21e4f72f5fa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_0eb3b6d1-5643-4830-815c-92a225563d33" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockholdersEquity_0eb3b6d1-5643-4830-815c-92a225563d33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_2c87bb1e-6d6f-44b6-8c0f-d1b5a724e84e" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_2c87bb1e-6d6f-44b6-8c0f-d1b5a724e84e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_58b8c664-e049-4944-a1be-cdc70af429ac" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_58b8c664-e049-4944-a1be-cdc70af429ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_7e2edcff-0854-461c-bdf3-04bfd7d2c622" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_7e2edcff-0854-461c-bdf3-04bfd7d2c622" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_4fce6482-19ae-480b-9619-034c3c6a03c2" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_4fce6482-19ae-480b-9619-034c3c6a03c2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_247da061-bfa0-4f86-b019-4ff4d1a8f2c7" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_247da061-bfa0-4f86-b019-4ff4d1a8f2c7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d136f038-de2c-4eed-a14b-3ed1d02efd54" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d136f038-de2c-4eed-a14b-3ed1d02efd54" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_185875f3-9cdc-4d29-a1ab-45085450389a" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_185875f3-9cdc-4d29-a1ab-45085450389a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_fbad4cc9-ed3c-4f73-ac2e-8a5623d0e321" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_fbad4cc9-ed3c-4f73-ac2e-8a5623d0e321" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_282ddd42-dc42-4e78-9fc6-66e5725374b2" 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_552ce567-3c43-4e89-acdf-89a44d900979" xlink:to="loc_us-gaap_NetIncomeLoss_282ddd42-dc42-4e78-9fc6-66e5725374b2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_81ea1b40-a106-4184-a596-ab53a6aace3d" 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_d04ed318-ee83-494c-9657-afac02fcfa80" 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_96f2b07f-5ede-42f8-bed2-107e913953fa" 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_51c2758b-acb2-4bd7-8501-f5b2801e62b1" xlink:to="loc_us-gaap_StatementTable_96f2b07f-5ede-42f8-bed2-107e913953fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ac11bd44-adaa-48ef-8871-2678e432fe39" 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_96f2b07f-5ede-42f8-bed2-107e913953fa" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ac11bd44-adaa-48ef-8871-2678e432fe39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ac11bd44-adaa-48ef-8871-2678e432fe39_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_ac11bd44-adaa-48ef-8871-2678e432fe39" xlink:to="loc_us-gaap_EquityComponentDomain_ac11bd44-adaa-48ef-8871-2678e432fe39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a90a7880-e908-4a7b-8340-883da268d245" 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_ac11bd44-adaa-48ef-8871-2678e432fe39" xlink:to="loc_us-gaap_EquityComponentDomain_a90a7880-e908-4a7b-8340-883da268d245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_82516bbf-8255-4b6d-948b-98beea8d7bb9" 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_a90a7880-e908-4a7b-8340-883da268d245" xlink:to="loc_us-gaap_CommonStockMember_82516bbf-8255-4b6d-948b-98beea8d7bb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_3b4394f5-f712-437e-ae9c-ac95bb2bc678" 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_a90a7880-e908-4a7b-8340-883da268d245" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_3b4394f5-f712-437e-ae9c-ac95bb2bc678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_5578ece2-d37e-4441-87db-9b8eebdd1d91" 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_a90a7880-e908-4a7b-8340-883da268d245" xlink:to="loc_us-gaap_RetainedEarningsMember_5578ece2-d37e-4441-87db-9b8eebdd1d91" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#RevenueDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="extended" id="ifdc5df5959764cb6bb47ce02115be045_RevenueDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_d3a12cf5-6b67-4909-99c2-ce097fdee44c" 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_1bfe8e13-07ab-4c40-9544-41c07335896b" 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_d3a12cf5-6b67-4909-99c2-ce097fdee44c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_1bfe8e13-07ab-4c40-9544-41c07335896b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_e3b8732b-1c94-409e-870e-752d7286e502" 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_d3a12cf5-6b67-4909-99c2-ce097fdee44c" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_e3b8732b-1c94-409e-870e-752d7286e502" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_44f952dc-5178-4246-885a-96f21383c031" 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_e3b8732b-1c94-409e-870e-752d7286e502" xlink:to="loc_srt_ProductOrServiceAxis_44f952dc-5178-4246-885a-96f21383c031" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_44f952dc-5178-4246-885a-96f21383c031_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_44f952dc-5178-4246-885a-96f21383c031" xlink:to="loc_srt_ProductsAndServicesDomain_44f952dc-5178-4246-885a-96f21383c031_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_0c795442-ec13-4348-b87b-147dbd7540d4" 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_44f952dc-5178-4246-885a-96f21383c031" xlink:to="loc_srt_ProductsAndServicesDomain_0c795442-ec13-4348-b87b-147dbd7540d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PlatformAndReferralFeesNetMember_d2c455a9-ea9f-4c40-8414-6a39bfc57d11" xlink:href="upst-20230331.xsd#upst_PlatformAndReferralFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_0c795442-ec13-4348-b87b-147dbd7540d4" xlink:to="loc_upst_PlatformAndReferralFeesNetMember_d2c455a9-ea9f-4c40-8414-6a39bfc57d11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingFeesNetMember_5543ee2b-d96d-4c6b-a564-5f92f175d0fe" xlink:href="upst-20230331.xsd#upst_ServicingFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_0c795442-ec13-4348-b87b-147dbd7540d4" xlink:to="loc_upst_ServicingFeesNetMember_5543ee2b-d96d-4c6b-a564-5f92f175d0fe" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueNarrativeDetails" xlink:type="extended" id="idd795c8ee5724df1a9fbc52b6ce2af21_RevenueNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_d131ab6f-b3ea-49f4-843e-704d34325fc5" 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_025a6f3a-4554-403c-96bf-e22ffada297d" xlink:href="upst-20230331.xsd#upst_LoanPremiumFeesAndLoanTrailingFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_upst_LoanPremiumFeesAndLoanTrailingFees_025a6f3a-4554-403c-96bf-e22ffada297d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_e052c906-9510-43ae-9440-99d7cbd0a943" xlink:href="upst-20230331.xsd#upst_TrailingFeeLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_e052c906-9510-43ae-9440-99d7cbd0a943" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedFeesAndOtherRevenueReceivable_8d5efc9f-6d0f-464f-9c7a-cffd4c59c480" 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_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_AccruedFeesAndOtherRevenueReceivable_8d5efc9f-6d0f-464f-9c7a-cffd4c59c480" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_a77abc87-921a-441e-89fb-c09baf316b15" 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_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_a77abc87-921a-441e-89fb-c09baf316b15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostNet_44ee993b-40e8-4a27-a8c3-5214df734049" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalizedContractCostNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_CapitalizedContractCostNet_44ee993b-40e8-4a27-a8c3-5214df734049" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_2e340857-cf08-4fe2-800c-e29b2e409cdf" 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_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_2e340857-cf08-4fe2-800c-e29b2e409cdf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_958ba4bc-5c4d-46f8-9086-99e8b60941e0" 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_DisaggregationOfRevenueLineItems_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_958ba4bc-5c4d-46f8-9086-99e8b60941e0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_8faa0be1-bf4d-4b58-aa91-7e1ff7c44854" 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_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_8faa0be1-bf4d-4b58-aa91-7e1ff7c44854" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_35c76389-3ca2-49a5-acdd-e88c782ad050" 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_d131ab6f-b3ea-49f4-843e-704d34325fc5" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_35c76389-3ca2-49a5-acdd-e88c782ad050" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a8ed41da-cad1-4464-833b-cbd10523ebd2" 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_35c76389-3ca2-49a5-acdd-e88c782ad050" xlink:to="loc_srt_ProductOrServiceAxis_a8ed41da-cad1-4464-833b-cbd10523ebd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a8ed41da-cad1-4464-833b-cbd10523ebd2_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_a8ed41da-cad1-4464-833b-cbd10523ebd2" xlink:to="loc_srt_ProductsAndServicesDomain_a8ed41da-cad1-4464-833b-cbd10523ebd2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_d399d8bc-744e-4558-bc18-5f7b20351679" 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_a8ed41da-cad1-4464-833b-cbd10523ebd2" xlink:to="loc_srt_ProductsAndServicesDomain_d399d8bc-744e-4558-bc18-5f7b20351679" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PlatformAndReferralFeesNetMember_9c8458f4-f5be-4bb8-8f9c-72f328c1096e" xlink:href="upst-20230331.xsd#upst_PlatformAndReferralFeesNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_d399d8bc-744e-4558-bc18-5f7b20351679" xlink:to="loc_upst_PlatformAndReferralFeesNetMember_9c8458f4-f5be-4bb8-8f9c-72f328c1096e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_023482db-0d37-485b-8b2e-ae1c86827bf0" 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_35c76389-3ca2-49a5-acdd-e88c782ad050" xlink:to="loc_srt_MajorCustomersAxis_023482db-0d37-485b-8b2e-ae1c86827bf0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_023482db-0d37-485b-8b2e-ae1c86827bf0_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_023482db-0d37-485b-8b2e-ae1c86827bf0" xlink:to="loc_srt_NameOfMajorCustomerDomain_023482db-0d37-485b-8b2e-ae1c86827bf0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_ef5c37f3-85b6-4be6-93c2-4dec86869a58" 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_023482db-0d37-485b-8b2e-ae1c86827bf0" xlink:to="loc_srt_NameOfMajorCustomerDomain_ef5c37f3-85b6-4be6-93c2-4dec86869a58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerAMember_3f0f0a50-deef-4e9c-9c0c-12aa697378eb" xlink:href="upst-20230331.xsd#upst_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ef5c37f3-85b6-4be6-93c2-4dec86869a58" xlink:to="loc_upst_CustomerAMember_3f0f0a50-deef-4e9c-9c0c-12aa697378eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerBMember_e6bac11f-697c-4b04-b2fb-e6bd336e2e6a" xlink:href="upst-20230331.xsd#upst_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ef5c37f3-85b6-4be6-93c2-4dec86869a58" xlink:to="loc_upst_CustomerBMember_e6bac11f-697c-4b04-b2fb-e6bd336e2e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerCMember_8e198849-586e-450c-b619-71de5ae329be" xlink:href="upst-20230331.xsd#upst_CustomerCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ef5c37f3-85b6-4be6-93c2-4dec86869a58" xlink:to="loc_upst_CustomerCMember_8e198849-586e-450c-b619-71de5ae329be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_aae51966-d683-464f-87f5-604d054ca762" 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_35c76389-3ca2-49a5-acdd-e88c782ad050" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_aae51966-d683-464f-87f5-604d054ca762" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_aae51966-d683-464f-87f5-604d054ca762_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_aae51966-d683-464f-87f5-604d054ca762" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_aae51966-d683-464f-87f5-604d054ca762_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_efd7b64f-0846-4a80-8a66-6a74a4f9191c" 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_aae51966-d683-464f-87f5-604d054ca762" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_efd7b64f-0846-4a80-8a66-6a74a4f9191c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_b354bf47-59f9-415f-ab24-51b109949aca" 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_efd7b64f-0846-4a80-8a66-6a74a4f9191c" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_b354bf47-59f9-415f-ab24-51b109949aca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d7ef999b-1ef4-45a2-98eb-e84d4276fb83" 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_35c76389-3ca2-49a5-acdd-e88c782ad050" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d7ef999b-1ef4-45a2-98eb-e84d4276fb83" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d7ef999b-1ef4-45a2-98eb-e84d4276fb83_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_d7ef999b-1ef4-45a2-98eb-e84d4276fb83" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d7ef999b-1ef4-45a2-98eb-e84d4276fb83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1996782b-e55f-47e2-987a-2027e50d9915" 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_d7ef999b-1ef4-45a2-98eb-e84d4276fb83" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1996782b-e55f-47e2-987a-2027e50d9915" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_7f984321-4248-4dc8-be79-051b42889db1" 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_1996782b-e55f-47e2-987a-2027e50d9915" xlink:to="loc_us-gaap_SalesRevenueNetMember_7f984321-4248-4dc8-be79-051b42889db1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_93f97aa7-1dee-4b2b-ae2f-90b26f55b521" 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_1996782b-e55f-47e2-987a-2027e50d9915" xlink:to="loc_us-gaap_AccountsReceivableMember_93f97aa7-1dee-4b2b-ae2f-90b26f55b521" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/RevenueFeesCollectedDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#RevenueFeesCollectedDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/RevenueFeesCollectedDetails" xlink:type="extended" id="i09776ddc6c0b4b38bdf630c08631a97c_RevenueFeesCollectedDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_082eab86-b66b-4d5b-b3a6-717831139f1b" 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_4615a793-f13c-4083-a46f-97079971a2b8" 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_082eab86-b66b-4d5b-b3a6-717831139f1b" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4615a793-f13c-4083-a46f-97079971a2b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_b97210a0-c366-4112-af28-f8ea6d18d03c" 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_082eab86-b66b-4d5b-b3a6-717831139f1b" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_b97210a0-c366-4112-af28-f8ea6d18d03c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576" 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_b97210a0-c366-4112-af28-f8ea6d18d03c" xlink:to="loc_srt_ProductOrServiceAxis_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576_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_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576" xlink:to="loc_srt_ProductsAndServicesDomain_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_222a0c13-aa17-413a-b53f-5fe5323fa7c2" 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_be4a8d72-5ff4-4c1c-8a83-2a9d88c28576" xlink:to="loc_srt_ProductsAndServicesDomain_222a0c13-aa17-413a-b53f-5fe5323fa7c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CollectionAgencyFeesMember_9d50d6be-b13a-4ef1-a37d-35d2ab1c7754" xlink:href="upst-20230331.xsd#upst_CollectionAgencyFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_222a0c13-aa17-413a-b53f-5fe5323fa7c2" xlink:to="loc_upst_CollectionAgencyFeesMember_9d50d6be-b13a-4ef1-a37d-35d2ab1c7754" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_BorrowerFeesMember_df388a4d-9c4f-47b4-8023-88d8f9015ccb" xlink:href="upst-20230331.xsd#upst_BorrowerFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_222a0c13-aa17-413a-b53f-5fe5323fa7c2" xlink:to="loc_upst_BorrowerFeesMember_df388a4d-9c4f-47b4-8023-88d8f9015ccb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/VariableInterestEntitiesAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#VariableInterestEntitiesAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/VariableInterestEntitiesAssetsandLiabilitiesDetails" xlink:type="extended" id="i653ec727e2254fdcb1076a400b06bc58_VariableInterestEntitiesAssetsandLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_4f861623-44ae-4ba1-b4dc-a0ebd406768e" 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_32665c7d-63fd-49f7-ae99-0e8fb3c67aea" 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_4f861623-44ae-4ba1-b4dc-a0ebd406768e" xlink:to="loc_us-gaap_Assets_32665c7d-63fd-49f7-ae99-0e8fb3c67aea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_419a05ea-786c-4deb-9233-310c766ef8f3" 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_4f861623-44ae-4ba1-b4dc-a0ebd406768e" xlink:to="loc_us-gaap_Liabilities_419a05ea-786c-4deb-9233-310c766ef8f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3d6e76ae-6df9-45bf-bd54-ef40ee817167" 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_4f861623-44ae-4ba1-b4dc-a0ebd406768e" xlink:to="loc_us-gaap_StockholdersEquity_3d6e76ae-6df9-45bf-bd54-ef40ee817167" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_42ca04f4-67b6-494b-ab56-85ee51fcf501" 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_4f861623-44ae-4ba1-b4dc-a0ebd406768e" xlink:to="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_42ca04f4-67b6-494b-ab56-85ee51fcf501" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_f35815a2-8a1f-4a21-ba1d-bcd17bdce79c" 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_4f861623-44ae-4ba1-b4dc-a0ebd406768e" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_f35815a2-8a1f-4a21-ba1d-bcd17bdce79c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_85f32f61-ada2-4c61-9285-20307fba3cac" 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_f35815a2-8a1f-4a21-ba1d-bcd17bdce79c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_85f32f61-ada2-4c61-9285-20307fba3cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_85f32f61-ada2-4c61-9285-20307fba3cac_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_85f32f61-ada2-4c61-9285-20307fba3cac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_85f32f61-ada2-4c61-9285-20307fba3cac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_43881cd2-e51f-45a6-94f5-e388d744b519" 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_85f32f61-ada2-4c61-9285-20307fba3cac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_43881cd2-e51f-45a6-94f5-e388d744b519" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_833d78f6-1815-46d3-bc48-98815b546038" 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_43881cd2-e51f-45a6-94f5-e388d744b519" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_833d78f6-1815-46d3-bc48-98815b546038" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_f38430c3-9a4e-45d8-a82a-a368c7b85536" 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_43881cd2-e51f-45a6-94f5-e388d744b519" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_f38430c3-9a4e-45d8-a82a-a368c7b85536" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_16e427ba-0a98-4e88-846f-e2fc661d2e87" 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_f35815a2-8a1f-4a21-ba1d-bcd17bdce79c" xlink:to="loc_srt_CounterpartyNameAxis_16e427ba-0a98-4e88-846f-e2fc661d2e87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_16e427ba-0a98-4e88-846f-e2fc661d2e87_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_16e427ba-0a98-4e88-846f-e2fc661d2e87" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_16e427ba-0a98-4e88-846f-e2fc661d2e87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_056b2206-f7f0-4b3f-a84b-295e7dfe123d" 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_16e427ba-0a98-4e88-846f-e2fc661d2e87" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_056b2206-f7f0-4b3f-a84b-295e7dfe123d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SecuritizationsMember_f49b2ddb-747f-4256-b76f-b37cd1ef0366" xlink:href="upst-20230331.xsd#upst_SecuritizationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_056b2206-f7f0-4b3f-a84b-295e7dfe123d" xlink:to="loc_upst_SecuritizationsMember_f49b2ddb-747f-4256-b76f-b37cd1ef0366" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/VariableInterestEntitiesNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#VariableInterestEntitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/VariableInterestEntitiesNarrativeDetails" xlink:type="extended" id="ib2d8ef13aa4a4aa4a2f1b7029f8616f4_VariableInterestEntitiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_82313f44-d85a-472b-a9e4-22f5f91fdd86" 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_upst_RiskRetentionRequirementDeclines_505a431d-a80b-47c1-9926-2c3e4bdd6953" xlink:href="upst-20230331.xsd#upst_RiskRetentionRequirementDeclines"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_82313f44-d85a-472b-a9e4-22f5f91fdd86" xlink:to="loc_upst_RiskRetentionRequirementDeclines_505a431d-a80b-47c1-9926-2c3e4bdd6953" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_b7d37dec-992a-41e7-b66d-959247e2ef52" 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_82313f44-d85a-472b-a9e4-22f5f91fdd86" xlink:to="loc_us-gaap_NotesReceivableNet_b7d37dec-992a-41e7-b66d-959247e2ef52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_5989c7df-052b-42fd-ad1c-f8c2b11e3378" 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_VariableInterestEntityLineItems_82313f44-d85a-472b-a9e4-22f5f91fdd86" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_5989c7df-052b-42fd-ad1c-f8c2b11e3378" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_7398390d-fdd5-410d-b9cb-f0d78d9f93ba" 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_82313f44-d85a-472b-a9e4-22f5f91fdd86" xlink:to="loc_us-gaap_RestrictedCash_7398390d-fdd5-410d-b9cb-f0d78d9f93ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_eeb8224c-906c-498b-8be7-5bfd8c77380a" 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_82313f44-d85a-472b-a9e4-22f5f91fdd86" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_eeb8224c-906c-498b-8be7-5bfd8c77380a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_ae34642e-ab36-4419-a339-a6a4377a1309" 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_eeb8224c-906c-498b-8be7-5bfd8c77380a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_ae34642e-ab36-4419-a339-a6a4377a1309" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_ae34642e-ab36-4419-a339-a6a4377a1309_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_ae34642e-ab36-4419-a339-a6a4377a1309" xlink:to="loc_srt_ConsolidatedEntitiesDomain_ae34642e-ab36-4419-a339-a6a4377a1309_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_5a738353-9716-4253-8105-7911066afc54" 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_ae34642e-ab36-4419-a339-a6a4377a1309" xlink:to="loc_srt_ConsolidatedEntitiesDomain_5a738353-9716-4253-8105-7911066afc54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_a33aab8e-c703-4f04-97f7-462b1ff6cc41" 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_5a738353-9716-4253-8105-7911066afc54" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_a33aab8e-c703-4f04-97f7-462b1ff6cc41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a57ad3ab-2fe0-4c30-998a-00063f3d9050" 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_eeb8224c-906c-498b-8be7-5bfd8c77380a" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_a57ad3ab-2fe0-4c30-998a-00063f3d9050" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_a57ad3ab-2fe0-4c30-998a-00063f3d9050_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_a57ad3ab-2fe0-4c30-998a-00063f3d9050" xlink:to="loc_us-gaap_ReceivableTypeDomain_a57ad3ab-2fe0-4c30-998a-00063f3d9050_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_fed811cf-c9f6-48f3-a5e2-144ff866e149" 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_a57ad3ab-2fe0-4c30-998a-00063f3d9050" xlink:to="loc_us-gaap_ReceivableTypeDomain_fed811cf-c9f6-48f3-a5e2-144ff866e149" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_NotesReceivableAndResidualCertificatesMember_5e51dd00-ab2b-4c6e-99bd-7558e0306fc3" xlink:href="upst-20230331.xsd#upst_NotesReceivableAndResidualCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_fed811cf-c9f6-48f3-a5e2-144ff866e149" xlink:to="loc_upst_NotesReceivableAndResidualCertificatesMember_5e51dd00-ab2b-4c6e-99bd-7558e0306fc3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/DerivativeFinancialInstrumentsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#DerivativeFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/DerivativeFinancialInstrumentsDetails" xlink:type="extended" id="i2ba421386da04c40a7cb1797e5d84740_DerivativeFinancialInstrumentsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_fd942d44-546f-46e5-99ed-7e781005285a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap_DerivativeNotionalAmount_fd942d44-546f-46e5-99ed-7e781005285a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCapInterestRate_0607807d-5d4a-424e-939c-76a0b94a6742" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeCapInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap_DerivativeCapInterestRate_0607807d-5d4a-424e-939c-76a0b94a6742" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-supplement_DerivativePremiumPaid_ebe3394a-3881-4e21-bb0d-7358413400a2" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_DerivativePremiumPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap-supplement_DerivativePremiumPaid_ebe3394a-3881-4e21-bb0d-7358413400a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_08c0eaca-84ac-4f1c-990e-dadc59d18a3e" 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_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_08c0eaca-84ac-4f1c-990e-dadc59d18a3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_ca3f4bdd-02ca-4b51-b3a2-cb5441dc4834" 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_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_ca3f4bdd-02ca-4b51-b3a2-cb5441dc4834" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_67f1ca6e-01b4-4558-8124-85a9b721a458" xlink:to="loc_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_e5584901-f163-4cf3-9e65-bffdcf88defc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_e5584901-f163-4cf3-9e65-bffdcf88defc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_e5584901-f163-4cf3-9e65-bffdcf88defc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e5584901-f163-4cf3-9e65-bffdcf88defc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_e5584901-f163-4cf3-9e65-bffdcf88defc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_88695775-9a03-45c4-9e19-def758daf941" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e5584901-f163-4cf3-9e65-bffdcf88defc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_88695775-9a03-45c4-9e19-def758daf941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_d86a9b3d-82e8-492f-b2c2-8f49f1a54458" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_88695775-9a03-45c4-9e19-def758daf941" xlink:to="loc_us-gaap_InterestRateCapMember_d86a9b3d-82e8-492f-b2c2-8f49f1a54458" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_WarehouseCreditFacilityMember_037df19b-c797-44c3-be08-d286a20b0d9a" xlink:href="upst-20230331.xsd#upst_WarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_88695775-9a03-45c4-9e19-def758daf941" xlink:to="loc_upst_WarehouseCreditFacilityMember_037df19b-c797-44c3-be08-d286a20b0d9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_20ee1799-990f-4472-ba97-2591f2cd69aa" 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_DerivativeContractTypeDomain_88695775-9a03-45c4-9e19-def758daf941" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_20ee1799-990f-4472-ba97-2591f2cd69aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1" 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_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:to="loc_srt_ConsolidatedEntitiesAxis_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1_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_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_5562cde6-2630-4b78-ad4b-067276a24311" 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_5c67b2e0-11c4-4cab-a79e-e885ca8e88f1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_5562cde6-2630-4b78-ad4b-067276a24311" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PrimaryBeneficiaryMember_c3b3dc05-eda7-46a9-9b04-aa20ac7186f5" xlink:href="upst-20230331.xsd#upst_PrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_5562cde6-2630-4b78-ad4b-067276a24311" xlink:to="loc_upst_PrimaryBeneficiaryMember_c3b3dc05-eda7-46a9-9b04-aa20ac7186f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_37952323-b75d-4dfe-9287-31aa620b6069" 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_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:to="loc_us-gaap_CreditFacilityAxis_37952323-b75d-4dfe-9287-31aa620b6069" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_37952323-b75d-4dfe-9287-31aa620b6069_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_37952323-b75d-4dfe-9287-31aa620b6069" xlink:to="loc_us-gaap_CreditFacilityDomain_37952323-b75d-4dfe-9287-31aa620b6069_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_9c163985-43da-4311-a343-458cf7058a52" 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_37952323-b75d-4dfe-9287-31aa620b6069" xlink:to="loc_us-gaap_CreditFacilityDomain_9c163985-43da-4311-a343-458cf7058a52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_3880eec6-5315-4d04-a3d0-e842003ae37e" 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_9c163985-43da-4311-a343-458cf7058a52" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_3880eec6-5315-4d04-a3d0-e842003ae37e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_af6038e2-eb60-46b9-b7d1-08034e9fa763" 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_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:to="loc_us-gaap_DebtInstrumentAxis_af6038e2-eb60-46b9-b7d1-08034e9fa763" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_af6038e2-eb60-46b9-b7d1-08034e9fa763_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_af6038e2-eb60-46b9-b7d1-08034e9fa763" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_af6038e2-eb60-46b9-b7d1-08034e9fa763_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_da35b59a-df3e-4fe4-86d0-6bcf98578881" 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_af6038e2-eb60-46b9-b7d1-08034e9fa763" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_da35b59a-df3e-4fe4-86d0-6bcf98578881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTWarehouseCreditFacilityMember_5794be3e-98f2-4217-b738-440a6e2c46c9" xlink:href="upst-20230331.xsd#upst_UAWTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da35b59a-df3e-4fe4-86d0-6bcf98578881" xlink:to="loc_upst_UAWTWarehouseCreditFacilityMember_5794be3e-98f2-4217-b738-440a6e2c46c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_4078aaa8-c69f-4f7f-9674-00fdd28257d2" 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_us-gaap_DerivativeTable_29bed82c-ac48-4815-a382-35cb00646749" xlink:to="loc_us-gaap_VariableRateAxis_4078aaa8-c69f-4f7f-9674-00fdd28257d2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_4078aaa8-c69f-4f7f-9674-00fdd28257d2_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_4078aaa8-c69f-4f7f-9674-00fdd28257d2" xlink:to="loc_us-gaap_VariableRateDomain_4078aaa8-c69f-4f7f-9674-00fdd28257d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_6cce6ed1-e85c-4594-8e32-8cb0e06af15c" 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_4078aaa8-c69f-4f7f-9674-00fdd28257d2" xlink:to="loc_us-gaap_VariableRateDomain_6cce6ed1-e85c-4594-8e32-8cb0e06af15c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SecuredOvernightFinancingRateSOFRMember_2064a4ad-b424-4e90-8ae2-2d69c29f5aa0" xlink:href="upst-20230331.xsd#upst_SecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_6cce6ed1-e85c-4594-8e32-8cb0e06af15c" xlink:to="loc_upst_SecuredOvernightFinancingRateSOFRMember_2064a4ad-b424-4e90-8ae2-2d69c29f5aa0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementAssetsandLiabilitiesDetails" xlink:type="extended" id="i9fb0eb997662425e93efd6b015c31006_FairValueMeasurementAssetsandLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_25ad5127-d5a1-4a6a-a785-63aeda2119da" 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_662f0f55-f5d3-4106-835f-ef5da056a204" 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_25ad5127-d5a1-4a6a-a785-63aeda2119da" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_288359ee-9043-4687-a0e1-ab0b5eb5fb03" 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_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_288359ee-9043-4687-a0e1-ab0b5eb5fb03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_b4f776f0-1b93-4d94-8b27-7d94237f6d8e" 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_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_b4f776f0-1b93-4d94-8b27-7d94237f6d8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_2097ec79-8838-4b3f-aed0-646e39aacb6c" 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_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_2097ec79-8838-4b3f-aed0-646e39aacb6c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_e337cee8-4274-4d96-82cd-91760cdbba3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:to="loc_us-gaap_DerivativeAssets_e337cee8-4274-4d96-82cd-91760cdbba3d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_9a68744c-f956-4b14-859a-b1b7fbedd6ef" 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_662f0f55-f5d3-4106-835f-ef5da056a204" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_9a68744c-f956-4b14-859a-b1b7fbedd6ef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_2e5cf72e-e9a8-4366-8aa6-3a6a2da73349" 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_25ad5127-d5a1-4a6a-a785-63aeda2119da" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_2e5cf72e-e9a8-4366-8aa6-3a6a2da73349" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_cf63e991-90b6-4384-8f02-df9f07583c64" 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_2e5cf72e-e9a8-4366-8aa6-3a6a2da73349" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_cf63e991-90b6-4384-8f02-df9f07583c64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_20bb9e5b-ae5b-4a92-8ce2-280e87d7ec1c" xlink:href="upst-20230331.xsd#upst_TrailingFeeLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_2e5cf72e-e9a8-4366-8aa6-3a6a2da73349" xlink:to="loc_upst_TrailingFeeLiabilitiesFairValueDisclosure_20bb9e5b-ae5b-4a92-8ce2-280e87d7ec1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_43e2e8af-3d04-4c93-99e9-c6db3d310d58" 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_2e5cf72e-e9a8-4366-8aa6-3a6a2da73349" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_43e2e8af-3d04-4c93-99e9-c6db3d310d58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_773dc65b-f10c-4214-8f47-f909487eefe2" 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_25ad5127-d5a1-4a6a-a785-63aeda2119da" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_773dc65b-f10c-4214-8f47-f909487eefe2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c595b536-5928-4b0a-b6aa-0bdfab146dbb" 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_773dc65b-f10c-4214-8f47-f909487eefe2" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_c595b536-5928-4b0a-b6aa-0bdfab146dbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c595b536-5928-4b0a-b6aa-0bdfab146dbb_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_c595b536-5928-4b0a-b6aa-0bdfab146dbb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c595b536-5928-4b0a-b6aa-0bdfab146dbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a2a09690-de66-42a6-adcb-c8bb661fbced" 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_c595b536-5928-4b0a-b6aa-0bdfab146dbb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a2a09690-de66-42a6-adcb-c8bb661fbced" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_51808028-5497-47dc-bd6d-824d4a582484" 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_a2a09690-de66-42a6-adcb-c8bb661fbced" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_51808028-5497-47dc-bd6d-824d4a582484" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_ce187a72-4283-404e-9b2b-dca17a2eedb7" 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_a2a09690-de66-42a6-adcb-c8bb661fbced" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_ce187a72-4283-404e-9b2b-dca17a2eedb7" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementNarrativeDetails" xlink:type="extended" id="if95a9425cd9845fd995d54fad64b56aa_FairValueMeasurementNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" 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_e54ba72f-1cbb-44ca-9ef7-2792bd62f460" 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_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_e54ba72f-1cbb-44ca-9ef7-2792bd62f460" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansHeldForInvestmentFairValueDisclosure_cb726657-d0ca-4bf7-a048-2fbf4245ed18" xlink:href="upst-20230331.xsd#upst_LoansHeldForInvestmentFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_LoansHeldForInvestmentFairValueDisclosure_cb726657-d0ca-4bf7-a048-2fbf4245ed18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_2b1540c0-fc54-490e-87c1-17b7d9f7eeb2" 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_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_2b1540c0-fc54-490e-87c1-17b7d9f7eeb2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff_f73a67d4-1b14-4cc8-b017-3c53dfa5d2b8" 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_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff_f73a67d4-1b14-4cc8-b017-3c53dfa5d2b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_368ce1a8-778e-429b-a8e1-4635e357aaa0" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_368ce1a8-778e-429b-a8e1-4635e357aaa0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_da1cc6ff-ecfa-48f7-9946-027d3215cbe4" 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_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_da1cc6ff-ecfa-48f7-9946-027d3215cbe4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage_3aeb961e-f8a7-4315-96d6-43cb9306e5e0" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRatesAverage_3aeb961e-f8a7-4315-96d6-43cb9306e5e0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage_f326a376-6d07-43d6-9b3d-799357313c9b" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRatesAverage_f326a376-6d07-43d6-9b3d-799357313c9b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage_ef32015e-0290-46be-ba32-cf7363c823fc" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRatesAverage_ef32015e-0290-46be-ba32-cf7363c823fc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansReceivableMeasurementInput_f440f03f-aab1-4727-81e7-bf254f1272a4" xlink:href="upst-20230331.xsd#upst_LoansReceivableMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_LoansReceivableMeasurementInput_f440f03f-aab1-4727-81e7-bf254f1272a4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeesLiabilityMeasurementInput_340c4739-b8d1-434b-9bf8-fdfc2ea2b165" xlink:href="upst-20230331.xsd#upst_TrailingFeesLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_upst_TrailingFeesLiabilityMeasurementInput_340c4739-b8d1-434b-9bf8-fdfc2ea2b165" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_759623a5-1c69-429f-8ea1-8332fb5f1505" 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_94d50327-c43a-46ee-a36d-71e8c691aef3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_dea51667-a47e-4e86-8189-9a3a1aee8137" 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_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_dea51667-a47e-4e86-8189-9a3a1aee8137" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_dea51667-a47e-4e86-8189-9a3a1aee8137_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_dea51667-a47e-4e86-8189-9a3a1aee8137" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_dea51667-a47e-4e86-8189-9a3a1aee8137_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ddce275e-3596-4006-ab82-694ba14ae00d" 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_dea51667-a47e-4e86-8189-9a3a1aee8137" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ddce275e-3596-4006-ab82-694ba14ae00d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_98210630-b3f0-4fb5-a4bb-a829fe8861e9" 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_ddce275e-3596-4006-ab82-694ba14ae00d" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_98210630-b3f0-4fb5-a4bb-a829fe8861e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1b63af55-38ae-4db9-9539-40f36827d262" 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_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:to="loc_srt_RangeAxis_1b63af55-38ae-4db9-9539-40f36827d262" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1b63af55-38ae-4db9-9539-40f36827d262_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_1b63af55-38ae-4db9-9539-40f36827d262" xlink:to="loc_srt_RangeMember_1b63af55-38ae-4db9-9539-40f36827d262_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_38c2ac10-7298-4721-a228-3b5e64b27e9e" 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_1b63af55-38ae-4db9-9539-40f36827d262" xlink:to="loc_srt_RangeMember_38c2ac10-7298-4721-a228-3b5e64b27e9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_16c7760c-5026-4b88-9e4e-5fabba6aea18" 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_38c2ac10-7298-4721-a228-3b5e64b27e9e" xlink:to="loc_srt_MinimumMember_16c7760c-5026-4b88-9e4e-5fabba6aea18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_48d57543-fbd6-4b30-b357-1b6d5d54da13" 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_38c2ac10-7298-4721-a228-3b5e64b27e9e" xlink:to="loc_srt_MaximumMember_48d57543-fbd6-4b30-b357-1b6d5d54da13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_0009308a-28f9-43a4-a8bb-e8fe02e5a7da" 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_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_0009308a-28f9-43a4-a8bb-e8fe02e5a7da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_0009308a-28f9-43a4-a8bb-e8fe02e5a7da_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_0009308a-28f9-43a4-a8bb-e8fe02e5a7da" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_0009308a-28f9-43a4-a8bb-e8fe02e5a7da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_5690d7ce-5061-4d0e-b1d2-37f292895cb0" 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_0009308a-28f9-43a4-a8bb-e8fe02e5a7da" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_5690d7ce-5061-4d0e-b1d2-37f292895cb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_053c106b-663e-403a-8869-4bb808291ba1" 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_5690d7ce-5061-4d0e-b1d2-37f292895cb0" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_053c106b-663e-403a-8869-4bb808291ba1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputEntityCreditRiskMember_c58852e6-9cce-4d8f-b142-0a5938289749" 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_5690d7ce-5061-4d0e-b1d2-37f292895cb0" xlink:to="loc_us-gaap_MeasurementInputEntityCreditRiskMember_c58852e6-9cce-4d8f-b142-0a5938289749" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_694bc012-25fc-4f48-bdb2-fe2668859ee7" 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_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_694bc012-25fc-4f48-bdb2-fe2668859ee7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_694bc012-25fc-4f48-bdb2-fe2668859ee7_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_694bc012-25fc-4f48-bdb2-fe2668859ee7" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_694bc012-25fc-4f48-bdb2-fe2668859ee7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2c399a75-a696-429f-a466-208e42c37939" 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_694bc012-25fc-4f48-bdb2-fe2668859ee7" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2c399a75-a696-429f-a466-208e42c37939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableMember_8cb80f36-a2a7-4de6-8ff7-0953bc2ec44b" 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_2c399a75-a696-429f-a466-208e42c37939" xlink:to="loc_us-gaap_NotesReceivableMember_8cb80f36-a2a7-4de6-8ff7-0953bc2ec44b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_c74a88b4-3bc7-4e6a-ba52-5c3fa3c43e20" 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_2c399a75-a696-429f-a466-208e42c37939" xlink:to="loc_us-gaap_LoansReceivableMember_c74a88b4-3bc7-4e6a-ba52-5c3fa3c43e20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UpstartPoweredPersonalLoansMember_8276c17c-6264-416c-bd74-a693a9d1be9e" xlink:href="upst-20230331.xsd#upst_UpstartPoweredPersonalLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2c399a75-a696-429f-a466-208e42c37939" xlink:to="loc_upst_UpstartPoweredPersonalLoansMember_8276c17c-6264-416c-bd74-a693a9d1be9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_73a3dc16-5f36-4373-b992-2dd883a402a6" 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_759623a5-1c69-429f-8ea1-8332fb5f1505" xlink:to="loc_us-gaap_ValuationTechniqueAxis_73a3dc16-5f36-4373-b992-2dd883a402a6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_73a3dc16-5f36-4373-b992-2dd883a402a6_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_73a3dc16-5f36-4373-b992-2dd883a402a6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_73a3dc16-5f36-4373-b992-2dd883a402a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_48f32ef8-d192-4f52-9c5b-442543fc68df" 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_73a3dc16-5f36-4373-b992-2dd883a402a6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_48f32ef8-d192-4f52-9c5b-442543fc68df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_67172aa5-25d6-4eaa-82a3-d4a907a4b65a" 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_48f32ef8-d192-4f52-9c5b-442543fc68df" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_67172aa5-25d6-4eaa-82a3-d4a907a4b65a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementSignificantInputsandAssumptionsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementSignificantInputsandAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementSignificantInputsandAssumptionsDetails" xlink:type="extended" id="ieff1df4b3bd34d22923ac6f6fce0f337_FairValueMeasurementSignificantInputsandAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_45f52921-bc32-40f0-846c-613c3563670f" 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_90144110-a136-4f59-a119-076a35b3b93a" xlink:href="upst-20230331.xsd#upst_LoansReceivableMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_45f52921-bc32-40f0-846c-613c3563670f" xlink:to="loc_upst_LoansReceivableMeasurementInput_90144110-a136-4f59-a119-076a35b3b93a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_6d6c2ffa-874f-457f-99f1-62f5afff6707" 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_45f52921-bc32-40f0-846c-613c3563670f" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_f3345e6b-3b9b-4913-8c25-47e2e864aa72" 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_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:to="loc_srt_RangeAxis_f3345e6b-3b9b-4913-8c25-47e2e864aa72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f3345e6b-3b9b-4913-8c25-47e2e864aa72_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_f3345e6b-3b9b-4913-8c25-47e2e864aa72" xlink:to="loc_srt_RangeMember_f3345e6b-3b9b-4913-8c25-47e2e864aa72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4aac5bba-efb4-4882-8959-06659fc95f02" 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_f3345e6b-3b9b-4913-8c25-47e2e864aa72" xlink:to="loc_srt_RangeMember_4aac5bba-efb4-4882-8959-06659fc95f02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_8c37df3d-2f60-48c4-9f1f-415f514f8844" 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_4aac5bba-efb4-4882-8959-06659fc95f02" xlink:to="loc_srt_MinimumMember_8c37df3d-2f60-48c4-9f1f-415f514f8844" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_b14b3772-3182-47ca-b5c8-a00ce60d499e" 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_4aac5bba-efb4-4882-8959-06659fc95f02" xlink:to="loc_srt_MaximumMember_b14b3772-3182-47ca-b5c8-a00ce60d499e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_db6b6dd6-83de-46a0-8eb6-4218c66cc0ac" 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_4aac5bba-efb4-4882-8959-06659fc95f02" xlink:to="loc_srt_WeightedAverageMember_db6b6dd6-83de-46a0-8eb6-4218c66cc0ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_64deddb6-19e8-400a-b226-4215f186e0ba" 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_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:to="loc_us-gaap_ValuationTechniqueAxis_64deddb6-19e8-400a-b226-4215f186e0ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_64deddb6-19e8-400a-b226-4215f186e0ba_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_64deddb6-19e8-400a-b226-4215f186e0ba" xlink:to="loc_us-gaap_ValuationTechniqueDomain_64deddb6-19e8-400a-b226-4215f186e0ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_67fdd1ae-0aa8-4674-92bd-58124f551386" 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_64deddb6-19e8-400a-b226-4215f186e0ba" xlink:to="loc_us-gaap_ValuationTechniqueDomain_67fdd1ae-0aa8-4674-92bd-58124f551386" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_fecc04fa-d6a2-4376-9900-2d15fa421a42" 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_67fdd1ae-0aa8-4674-92bd-58124f551386" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_fecc04fa-d6a2-4376-9900-2d15fa421a42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b28dc442-d45b-4579-80ae-d3b15137c37f" 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_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b28dc442-d45b-4579-80ae-d3b15137c37f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b28dc442-d45b-4579-80ae-d3b15137c37f_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_b28dc442-d45b-4579-80ae-d3b15137c37f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b28dc442-d45b-4579-80ae-d3b15137c37f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f724b7df-40a2-4d6a-97af-cc35dc3c1870" 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_b28dc442-d45b-4579-80ae-d3b15137c37f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f724b7df-40a2-4d6a-97af-cc35dc3c1870" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_2f12acd0-f51c-4a1d-9ab5-e15de36a59d1" 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_f724b7df-40a2-4d6a-97af-cc35dc3c1870" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_2f12acd0-f51c-4a1d-9ab5-e15de36a59d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_68f5a61b-94ae-4e8f-81a5-9ae03f17be56" 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_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_68f5a61b-94ae-4e8f-81a5-9ae03f17be56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_68f5a61b-94ae-4e8f-81a5-9ae03f17be56_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_68f5a61b-94ae-4e8f-81a5-9ae03f17be56" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_68f5a61b-94ae-4e8f-81a5-9ae03f17be56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_e66c60f9-44d7-40fc-8a87-72b84c548f8d" 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_68f5a61b-94ae-4e8f-81a5-9ae03f17be56" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_e66c60f9-44d7-40fc-8a87-72b84c548f8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_0e6778f1-681e-4122-98e1-c43272b4cb34" 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_e66c60f9-44d7-40fc-8a87-72b84c548f8d" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_0e6778f1-681e-4122-98e1-c43272b4cb34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputEntityCreditRiskMember_f86efe4f-a7c2-47c4-9a43-239e35c108f5" 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_e66c60f9-44d7-40fc-8a87-72b84c548f8d" xlink:to="loc_us-gaap_MeasurementInputEntityCreditRiskMember_f86efe4f-a7c2-47c4-9a43-239e35c108f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPrepaymentRateMember_7e0651b1-750d-44d9-8332-47ef9a976cdc" 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_e66c60f9-44d7-40fc-8a87-72b84c548f8d" xlink:to="loc_us-gaap_MeasurementInputPrepaymentRateMember_7e0651b1-750d-44d9-8332-47ef9a976cdc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_8517c49f-0fb0-40bd-bb37-dfd770aa84ad" 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_6d6c2ffa-874f-457f-99f1-62f5afff6707" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_8517c49f-0fb0-40bd-bb37-dfd770aa84ad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8517c49f-0fb0-40bd-bb37-dfd770aa84ad_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_8517c49f-0fb0-40bd-bb37-dfd770aa84ad" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_8517c49f-0fb0-40bd-bb37-dfd770aa84ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1d4b65d0-19e0-43c8-bfea-090945504d75" 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_8517c49f-0fb0-40bd-bb37-dfd770aa84ad" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1d4b65d0-19e0-43c8-bfea-090945504d75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_548b15d2-a427-49d4-a421-d5cf2e0465a1" 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_1d4b65d0-19e0-43c8-bfea-090945504d75" xlink:to="loc_us-gaap_LoansReceivableMember_548b15d2-a427-49d4-a421-d5cf2e0465a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableMember_3ed2706c-a785-4c9f-8465-ce225ff9612e" 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_1d4b65d0-19e0-43c8-bfea-090945504d75" xlink:to="loc_us-gaap_NotesReceivableMember_3ed2706c-a785-4c9f-8465-ce225ff9612e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementSensitivityofFairValueDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementSensitivityofFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementSensitivityofFairValueDetails" xlink:type="extended" id="ie988ba11d0604656b84cdeb4b38acbbe_FairValueMeasurementSensitivityofFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_9b153664-988f-423a-aeea-4e0f85f4b005" 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_cbb0e03d-d1e7-456a-86c0-d06d85cd8eac" 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_9b153664-988f-423a-aeea-4e0f85f4b005" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_cbb0e03d-d1e7-456a-86c0-d06d85cd8eac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DiscountRateAbstract_d2a7d807-b099-41bc-94ab-0cd7c1eb948d" xlink:href="upst-20230331.xsd#upst_DiscountRateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_9b153664-988f-423a-aeea-4e0f85f4b005" xlink:to="loc_upst_DiscountRateAbstract_d2a7d807-b099-41bc-94ab-0cd7c1eb948d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates_75349707-38a6-4fcf-835b-6f4ef13b8cbd" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DiscountRateAbstract_d2a7d807-b099-41bc-94ab-0cd7c1eb948d" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf100BasisPointIncreaseInDiscountRates_75349707-38a6-4fcf-835b-6f4ef13b8cbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates_559eaa2d-f49f-42cf-bb63-6eddf68af4b9" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DiscountRateAbstract_d2a7d807-b099-41bc-94ab-0cd7c1eb948d" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf200BasisPointIncreaseInDiscountRates_559eaa2d-f49f-42cf-bb63-6eddf68af4b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ExpectedCreditLossRateAbstract_c3e29b86-6587-4751-b50c-002ea9dc9e66" xlink:href="upst-20230331.xsd#upst_ExpectedCreditLossRateAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_9b153664-988f-423a-aeea-4e0f85f4b005" xlink:to="loc_upst_ExpectedCreditLossRateAbstract_c3e29b86-6587-4751-b50c-002ea9dc9e66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates_f39ad663-0b21-4df1-8048-539d75c7fdc7" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedCreditLossRateAbstract_c3e29b86-6587-4751-b50c-002ea9dc9e66" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedCreditLossRates_f39ad663-0b21-4df1-8048-539d75c7fdc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates_fac7b58b-97f0-4432-ad09-b2107596acc0" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedCreditLossRateAbstract_c3e29b86-6587-4751-b50c-002ea9dc9e66" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedCreditLossRates_fac7b58b-97f0-4432-ad09-b2107596acc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ExpectedPrepaymentRatesAbstract_f36b2c4b-3229-4b88-a2da-5ce35c475199" xlink:href="upst-20230331.xsd#upst_ExpectedPrepaymentRatesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_9b153664-988f-423a-aeea-4e0f85f4b005" xlink:to="loc_upst_ExpectedPrepaymentRatesAbstract_f36b2c4b-3229-4b88-a2da-5ce35c475199" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates_4dd30cc1-d5d8-4f5c-be5f-0855901d1b87" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedPrepaymentRatesAbstract_f36b2c4b-3229-4b88-a2da-5ce35c475199" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf10PercentAdverseChangeInExpectedPrepaymentRates_4dd30cc1-d5d8-4f5c-be5f-0855901d1b87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates_d66ca11c-39f8-42b9-a1e9-815532da2de5" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ExpectedPrepaymentRatesAbstract_f36b2c4b-3229-4b88-a2da-5ce35c475199" xlink:to="loc_upst_SensitivityAnalysisOfFairValueAssetsImpactOf20PercentAdverseChangeInExpectedPrepaymentRates_d66ca11c-39f8-42b9-a1e9-815532da2de5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_70c313c3-4af3-4fa8-b7ed-b631d07eada0" 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_9b153664-988f-423a-aeea-4e0f85f4b005" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_70c313c3-4af3-4fa8-b7ed-b631d07eada0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e45994d1-953e-4843-8f1d-c0a5979d5e91" 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_70c313c3-4af3-4fa8-b7ed-b631d07eada0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e45994d1-953e-4843-8f1d-c0a5979d5e91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_e45994d1-953e-4843-8f1d-c0a5979d5e91_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_e45994d1-953e-4843-8f1d-c0a5979d5e91" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_e45994d1-953e-4843-8f1d-c0a5979d5e91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c25d599a-a02f-4594-9fcc-ba20504a22f9" 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_e45994d1-953e-4843-8f1d-c0a5979d5e91" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c25d599a-a02f-4594-9fcc-ba20504a22f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_214a8ad4-42c7-4e67-b1b2-82f1df769e45" 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_c25d599a-a02f-4594-9fcc-ba20504a22f9" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_214a8ad4-42c7-4e67-b1b2-82f1df769e45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_a330bf94-c1e9-4f81-85be-084db3282c73" 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_70c313c3-4af3-4fa8-b7ed-b631d07eada0" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_a330bf94-c1e9-4f81-85be-084db3282c73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a330bf94-c1e9-4f81-85be-084db3282c73_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_a330bf94-c1e9-4f81-85be-084db3282c73" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a330bf94-c1e9-4f81-85be-084db3282c73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_d2db0d09-c258-4c18-a0e9-493ec1752117" 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_a330bf94-c1e9-4f81-85be-084db3282c73" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_d2db0d09-c258-4c18-a0e9-493ec1752117" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_8c384b32-b7ea-4793-bc2e-9916cdc4fae3" 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_d2db0d09-c258-4c18-a0e9-493ec1752117" xlink:to="loc_us-gaap_LoansReceivableMember_8c384b32-b7ea-4793-bc2e-9916cdc4fae3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoansRollforwardDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementLoansRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoansRollforwardDetails" xlink:type="extended" id="i9beeb377c8fe491a90b2090571865c23_FairValueMeasurementLoansRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_612ed49a-27d0-4fe4-9fcf-6a71f71d027b" 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_728142ac-8565-43e7-bf85-d4f9eed23e39" 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_612ed49a-27d0-4fe4-9fcf-6a71f71d027b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_8d05c9a6-3f12-4228-972b-770ea12d99bb" 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_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_8d05c9a6-3f12-4228-972b-770ea12d99bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification_aff8d936-7655-4367-8c6b-76a27207b532" xlink:href="upst-20230331.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetReclassification_aff8d936-7655-4367-8c6b-76a27207b532" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_84f27ce6-09bf-474d-b541-410202292e0f" 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_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_84f27ce6-09bf-474d-b541-410202292e0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_5df0ccce-4bb7-4070-a6aa-6402df20b9dc" 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_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_5df0ccce-4bb7-4070-a6aa-6402df20b9dc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors_9592aae4-3016-4482-b3b0-a1480209142c" xlink:href="upst-20230331.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfLoansForImmediateResaleToInvestors_9592aae4-3016-4482-b3b0-a1480209142c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors_b84a6e3f-9172-489a-8987-2676ba719dca" xlink:href="upst-20230331.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImmediateResaleToInvestors_b84a6e3f-9172-489a-8987-2676ba719dca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived_4775d771-642f-40be-94ae-35cfa8bcb294" xlink:href="upst-20230331.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRepaymentsReceived_4775d771-642f-40be-94ae-35cfa8bcb294" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_4c7dab79-4f17-49be-86d2-1fa14d1ee5d1" 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_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_4c7dab79-4f17-49be-86d2-1fa14d1ee5d1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease_eff195c5-14af-438b-99b1-e33967047761" xlink:href="upst-20230331.xsd#upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_728142ac-8565-43e7-bf85-d4f9eed23e39" xlink:to="loc_upst_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherIncreaseDecrease_eff195c5-14af-438b-99b1-e33967047761" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_a5b0b541-6af2-4577-978c-758065f20992" 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_a4fd4d47-38d4-4eca-9929-cea24b0d03d3" 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_612ed49a-27d0-4fe4-9fcf-6a71f71d027b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_a4fd4d47-38d4-4eca-9929-cea24b0d03d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d" 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_a4fd4d47-38d4-4eca-9929-cea24b0d03d3" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d_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_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_0c57609e-b07d-4fa6-8819-b5936ced9fbd" 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_16b0c651-5fa7-483b-a7d0-e2c2bb3e939d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_0c57609e-b07d-4fa6-8819-b5936ced9fbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_8e55ea54-a3f9-4744-a972-c0ce75ada949" 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_0c57609e-b07d-4fa6-8819-b5936ced9fbd" xlink:to="loc_us-gaap_LoansReceivableMember_8e55ea54-a3f9-4744-a972-c0ce75ada949" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanHeldForSaleMember_33f66aac-958e-4ffc-aa28-03c91a7b59d4" xlink:href="upst-20230331.xsd#upst_LoanHeldForSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoansReceivableMember_8e55ea54-a3f9-4744-a972-c0ce75ada949" xlink:to="loc_upst_LoanHeldForSaleMember_33f66aac-958e-4ffc-aa28-03c91a7b59d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoansHeldForInvestmentMember_4540f235-f07d-4d69-8376-1ead9f8628dc" xlink:href="upst-20230331.xsd#upst_LoansHeldForInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoansReceivableMember_8e55ea54-a3f9-4744-a972-c0ce75ada949" xlink:to="loc_upst_LoansHeldForInvestmentMember_4540f235-f07d-4d69-8376-1ead9f8628dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4bade969-4fcd-48a1-97f6-df93009af8e3" 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_a4fd4d47-38d4-4eca-9929-cea24b0d03d3" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4bade969-4fcd-48a1-97f6-df93009af8e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4bade969-4fcd-48a1-97f6-df93009af8e3_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_4bade969-4fcd-48a1-97f6-df93009af8e3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4bade969-4fcd-48a1-97f6-df93009af8e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cbe65fed-b538-4539-a387-d7b7916c8ef2" 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_4bade969-4fcd-48a1-97f6-df93009af8e3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cbe65fed-b538-4539-a387-d7b7916c8ef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_fc8aa599-14cb-4cc4-90b0-19170fd741d6" 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_cbe65fed-b538-4539-a387-d7b7916c8ef2" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_fc8aa599-14cb-4cc4-90b0-19170fd741d6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoansatFairValueDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementLoansatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoansatFairValueDetails" xlink:type="extended" id="i7ae7f64742374f5496cbeb4296245bbf_FairValueMeasurementLoansatFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_be778c0c-391a-47f8-a907-f074cee0c5fd" 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_0c4a0d5b-05b2-42bc-a7c2-196687a70361" 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_be778c0c-391a-47f8-a907-f074cee0c5fd" xlink:to="loc_us-gaap_NotesReceivableGross_0c4a0d5b-05b2-42bc-a7c2-196687a70361" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_183f6ede-5c13-46f8-9ce0-959621a0d936" 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_be778c0c-391a-47f8-a907-f074cee0c5fd" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_183f6ede-5c13-46f8-9ce0-959621a0d936" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_d160c709-a38f-4afe-b07d-a62f5e8784d2" 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_be778c0c-391a-47f8-a907-f074cee0c5fd" xlink:to="loc_us-gaap_NotesReceivableNet_d160c709-a38f-4afe-b07d-a62f5e8784d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_357f4de7-b14e-40f0-936d-a4768a152b94" 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_be778c0c-391a-47f8-a907-f074cee0c5fd" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_357f4de7-b14e-40f0-936d-a4768a152b94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0bdbc7d4-028b-423f-906e-4e1dfbc4c356" 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_357f4de7-b14e-40f0-936d-a4768a152b94" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_0bdbc7d4-028b-423f-906e-4e1dfbc4c356" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_0bdbc7d4-028b-423f-906e-4e1dfbc4c356_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_0bdbc7d4-028b-423f-906e-4e1dfbc4c356" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_0bdbc7d4-028b-423f-906e-4e1dfbc4c356_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_6fe74a36-b1b2-4b55-9ff3-b96f6adba7f8" 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_0bdbc7d4-028b-423f-906e-4e1dfbc4c356" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_6fe74a36-b1b2-4b55-9ff3-b96f6adba7f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_fd2a6807-f142-4019-ba5f-6c9971faa65f" 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_6fe74a36-b1b2-4b55-9ff3-b96f6adba7f8" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_fd2a6807-f142-4019-ba5f-6c9971faa65f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_7e48cb0b-077e-4a1d-bdf0-025be7c1d483" 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_357f4de7-b14e-40f0-936d-a4768a152b94" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_7e48cb0b-077e-4a1d-bdf0-025be7c1d483" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_7e48cb0b-077e-4a1d-bdf0-025be7c1d483_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_7e48cb0b-077e-4a1d-bdf0-025be7c1d483" xlink:to="loc_us-gaap_ReceivableTypeDomain_7e48cb0b-077e-4a1d-bdf0-025be7c1d483_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_a96e4aa8-206e-4906-92a3-77c5847a276e" 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_7e48cb0b-077e-4a1d-bdf0-025be7c1d483" xlink:to="loc_us-gaap_ReceivableTypeDomain_a96e4aa8-206e-4906-92a3-77c5847a276e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableMember_d505c3ed-da8f-4ecf-9556-e7524da90b92" 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_a96e4aa8-206e-4906-92a3-77c5847a276e" xlink:to="loc_us-gaap_LoansReceivableMember_d505c3ed-da8f-4ecf-9556-e7524da90b92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_080eb033-3218-435d-9741-b0e88436b5fa" 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_357f4de7-b14e-40f0-936d-a4768a152b94" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_080eb033-3218-435d-9741-b0e88436b5fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_080eb033-3218-435d-9741-b0e88436b5fa_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_080eb033-3218-435d-9741-b0e88436b5fa" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_080eb033-3218-435d-9741-b0e88436b5fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_50bbedc6-899b-4a81-bbae-36abdee0e502" 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_080eb033-3218-435d-9741-b0e88436b5fa" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_50bbedc6-899b-4a81-bbae-36abdee0e502" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AutoLoansMember_78f17b70-effe-4478-b440-61b4c1448b47" xlink:href="upst-20230331.xsd#upst_AutoLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_50bbedc6-899b-4a81-bbae-36abdee0e502" xlink:to="loc_upst_AutoLoansMember_78f17b70-effe-4478-b440-61b4c1448b47" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementNoteReceivableRollforwardDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementNoteReceivableRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementNoteReceivableRollforwardDetails" xlink:type="extended" id="i80a53a53fbb949ef8f7ebb922e45c76f_FairValueMeasurementNoteReceivableRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_58dbe41c-127b-4d1d-bb9e-af43b878f405" 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_39c11472-5493-48c1-9b21-26bd9c9ce3af" 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_58dbe41c-127b-4d1d-bb9e-af43b878f405" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_39c11472-5493-48c1-9b21-26bd9c9ce3af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_bd07eb6a-e1a6-4aca-8aaf-32b449b0f25a" 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_39c11472-5493-48c1-9b21-26bd9c9ce3af" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_bd07eb6a-e1a6-4aca-8aaf-32b449b0f25a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_33d301e9-6b35-483c-8af7-701dfb5220fd" 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_39c11472-5493-48c1-9b21-26bd9c9ce3af" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_33d301e9-6b35-483c-8af7-701dfb5220fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_201382fe-3895-4a9e-bb21-18ae580ffb91" 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_39c11472-5493-48c1-9b21-26bd9c9ce3af" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_201382fe-3895-4a9e-bb21-18ae580ffb91" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_471cceb7-2db7-4e17-8768-e7a2d752f4d8" 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_7ef15a95-7f13-4633-9e50-61e4f23c9e25" 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_58dbe41c-127b-4d1d-bb9e-af43b878f405" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_7ef15a95-7f13-4633-9e50-61e4f23c9e25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_49f297b7-f6cb-4447-a68a-762dee160fb4" 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_7ef15a95-7f13-4633-9e50-61e4f23c9e25" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_49f297b7-f6cb-4447-a68a-762dee160fb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_49f297b7-f6cb-4447-a68a-762dee160fb4_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_49f297b7-f6cb-4447-a68a-762dee160fb4" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_49f297b7-f6cb-4447-a68a-762dee160fb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6a203ef-8005-4d0c-985d-c0ff2043c91d" 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_49f297b7-f6cb-4447-a68a-762dee160fb4" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6a203ef-8005-4d0c-985d-c0ff2043c91d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_NotesReceivableAndResidualCertificatesMember_dae3749c-0dfd-48a6-a920-b98a2a4425c2" xlink:href="upst-20230331.xsd#upst_NotesReceivableAndResidualCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6a203ef-8005-4d0c-985d-c0ff2043c91d" xlink:to="loc_upst_NotesReceivableAndResidualCertificatesMember_dae3749c-0dfd-48a6-a920-b98a2a4425c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8b553de5-e405-4bfc-8d07-6d7f3f308002" 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_7ef15a95-7f13-4633-9e50-61e4f23c9e25" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8b553de5-e405-4bfc-8d07-6d7f3f308002" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8b553de5-e405-4bfc-8d07-6d7f3f308002_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_8b553de5-e405-4bfc-8d07-6d7f3f308002" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8b553de5-e405-4bfc-8d07-6d7f3f308002_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c130daca-6366-412f-9119-8480fb879528" 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_8b553de5-e405-4bfc-8d07-6d7f3f308002" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c130daca-6366-412f-9119-8480fb879528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_c3f9c84b-2798-47c6-a704-ca9f7f008964" 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_c130daca-6366-412f-9119-8480fb879528" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_c3f9c84b-2798-47c6-a704-ca9f7f008964" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementFairValueAssumptionsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementFairValueAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementFairValueAssumptionsDetails" xlink:type="extended" id="ia1cb9c7eaf674ffb9599916eb0d90429_FairValueMeasurementFairValueAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_8795e6e0-1440-49a1-b43d-52324262c1e8" 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_a78e8d78-7f69-4efd-bf3b-d88983b2fedb" 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_8795e6e0-1440-49a1-b43d-52324262c1e8" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate_a78e8d78-7f69-4efd-bf3b-d88983b2fedb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesExpectedCreditLosses_173825fc-3e72-42de-92a5-f25735099a28" 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_8795e6e0-1440-49a1-b43d-52324262c1e8" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesExpectedCreditLosses_173825fc-3e72-42de-92a5-f25735099a28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate_0a5848e3-c533-43dd-bda6-8fd36632c247" xlink:href="upst-20230331.xsd#upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems_8795e6e0-1440-49a1-b43d-52324262c1e8" xlink:to="loc_upst_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementMarketServicingRate_0a5848e3-c533-43dd-bda6-8fd36632c247" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed_a48ff3d7-12e9-48fe-809e-7f7c5e8ad965" 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_8795e6e0-1440-49a1-b43d-52324262c1e8" xlink:to="loc_us-gaap_AssumptionForFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed_a48ff3d7-12e9-48fe-809e-7f7c5e8ad965" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_96514e2a-3203-462b-b0c5-c8c317555b63" 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_8795e6e0-1440-49a1-b43d-52324262c1e8" xlink:to="loc_us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_96514e2a-3203-462b-b0c5-c8c317555b63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_325b9cac-bb04-43bb-9afa-9b7a2418a3c9" 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_96514e2a-3203-462b-b0c5-c8c317555b63" xlink:to="loc_srt_RangeAxis_325b9cac-bb04-43bb-9afa-9b7a2418a3c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_325b9cac-bb04-43bb-9afa-9b7a2418a3c9_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_325b9cac-bb04-43bb-9afa-9b7a2418a3c9" xlink:to="loc_srt_RangeMember_325b9cac-bb04-43bb-9afa-9b7a2418a3c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8c8a70e4-d5d6-44f9-8a33-b66318c58b10" 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_325b9cac-bb04-43bb-9afa-9b7a2418a3c9" xlink:to="loc_srt_RangeMember_8c8a70e4-d5d6-44f9-8a33-b66318c58b10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_24cdf579-14ff-4b23-8593-b67ebae77415" 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_8c8a70e4-d5d6-44f9-8a33-b66318c58b10" xlink:to="loc_srt_MinimumMember_24cdf579-14ff-4b23-8593-b67ebae77415" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_64a20088-3c1a-49c0-a5ba-b1714649bb47" 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_8c8a70e4-d5d6-44f9-8a33-b66318c58b10" xlink:to="loc_srt_MaximumMember_64a20088-3c1a-49c0-a5ba-b1714649bb47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_77268433-443c-4b05-8286-c4ebae54d1c7" 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_8c8a70e4-d5d6-44f9-8a33-b66318c58b10" xlink:to="loc_srt_WeightedAverageMember_77268433-443c-4b05-8286-c4ebae54d1c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_588c85f5-701a-4b3a-aa47-7b6d09e84ccf" 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_96514e2a-3203-462b-b0c5-c8c317555b63" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_588c85f5-701a-4b3a-aa47-7b6d09e84ccf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_588c85f5-701a-4b3a-aa47-7b6d09e84ccf_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_588c85f5-701a-4b3a-aa47-7b6d09e84ccf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_588c85f5-701a-4b3a-aa47-7b6d09e84ccf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f25aa5f5-e0b1-4bd0-960c-29e9c8b52c6d" 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_588c85f5-701a-4b3a-aa47-7b6d09e84ccf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f25aa5f5-e0b1-4bd0-960c-29e9c8b52c6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_2abd4b83-9f47-475c-a3dd-d20b98ca5d96" 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_f25aa5f5-e0b1-4bd0-960c-29e9c8b52c6d" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_2abd4b83-9f47-475c-a3dd-d20b98ca5d96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_512d5f87-86d3-401c-9367-b3660f70fd8e" 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_96514e2a-3203-462b-b0c5-c8c317555b63" xlink:to="loc_us-gaap_ValuationTechniqueAxis_512d5f87-86d3-401c-9367-b3660f70fd8e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_512d5f87-86d3-401c-9367-b3660f70fd8e_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_512d5f87-86d3-401c-9367-b3660f70fd8e" xlink:to="loc_us-gaap_ValuationTechniqueDomain_512d5f87-86d3-401c-9367-b3660f70fd8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_8bd03a09-22a2-4db2-b17f-24491aa1553d" 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_512d5f87-86d3-401c-9367-b3660f70fd8e" xlink:to="loc_us-gaap_ValuationTechniqueDomain_8bd03a09-22a2-4db2-b17f-24491aa1553d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_ef546cc6-062c-4fc4-be63-5eed9a0d6d88" 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_8bd03a09-22a2-4db2-b17f-24491aa1553d" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_ef546cc6-062c-4fc4-be63-5eed9a0d6d88" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingSensitivityDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementLoanServicingSensitivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingSensitivityDetails" xlink:type="extended" id="i902cbcb324ac49ab840d3f1e994291df_FairValueMeasurementLoanServicingSensitivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_6b8b855c-98ba-415c-ab07-c12b12f591ab" 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_d70ed6e6-37c4-4b1c-91f4-7364f4411ad8" 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_6b8b855c-98ba-415c-ab07-c12b12f591ab" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_d70ed6e6-37c4-4b1c-91f4-7364f4411ad8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_f6267d98-3cf6-44bb-8c6e-b6ae9f0376f5" 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_6b8b855c-98ba-415c-ab07-c12b12f591ab" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_f6267d98-3cf6-44bb-8c6e-b6ae9f0376f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates_91c4fa2c-f51e-4b00-b156-ad5e7f09bfc2" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_6b8b855c-98ba-415c-ab07-c12b12f591ab" xlink:to="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf10PercentIncreaseInMarketServicingRates_91c4fa2c-f51e-4b00-b156-ad5e7f09bfc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates_7f0bdd1d-a154-484c-89c2-eb7f8c1b681c" xlink:href="upst-20230331.xsd#upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfAdverseChangeInAssumptionLineItems_6b8b855c-98ba-415c-ab07-c12b12f591ab" xlink:to="loc_upst_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsImpactOf20PercentIncreaseInMarketServicingRates_7f0bdd1d-a154-484c-89c2-eb7f8c1b681c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_edc72fba-073e-434d-a4c1-08fefe29951a" 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_6b8b855c-98ba-415c-ab07-c12b12f591ab" xlink:to="loc_us-gaap_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesTable_edc72fba-073e-434d-a4c1-08fefe29951a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb" 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_edc72fba-073e-434d-a4c1-08fefe29951a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb_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_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7c605c9a-0192-4e55-b1e2-68c4d5733e81" 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_ddf9fec5-3f9b-40bf-a790-807b21ab6ecb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7c605c9a-0192-4e55-b1e2-68c4d5733e81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_795b2726-af41-4e6a-892f-15da7c9fefb5" 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_7c605c9a-0192-4e55-b1e2-68c4d5733e81" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_795b2726-af41-4e6a-892f-15da7c9fefb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_e6dd2794-d136-4e62-a089-b25e5ad6f789" 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_edc72fba-073e-434d-a4c1-08fefe29951a" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_e6dd2794-d136-4e62-a089-b25e5ad6f789" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6dd2794-d136-4e62-a089-b25e5ad6f789_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_e6dd2794-d136-4e62-a089-b25e5ad6f789" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6dd2794-d136-4e62-a089-b25e5ad6f789_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_fdbe6d85-6e6d-4446-a086-a4098a5d895f" 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_e6dd2794-d136-4e62-a089-b25e5ad6f789" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_fdbe6d85-6e6d-4446-a086-a4098a5d895f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingAssetsMember_aee60e48-7845-4af7-bdc2-09d6c72492b7" xlink:href="upst-20230331.xsd#upst_LoanServicingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_fdbe6d85-6e6d-4446-a086-a4098a5d895f" xlink:to="loc_upst_LoanServicingAssetsMember_aee60e48-7845-4af7-bdc2-09d6c72492b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_5b028af8-09d8-47e2-9bdb-41e198892cc5" 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_edc72fba-073e-434d-a4c1-08fefe29951a" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_5b028af8-09d8-47e2-9bdb-41e198892cc5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_5b028af8-09d8-47e2-9bdb-41e198892cc5_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_5b028af8-09d8-47e2-9bdb-41e198892cc5" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_5b028af8-09d8-47e2-9bdb-41e198892cc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9cd80fea-5dfb-4221-84f1-b169848f56e5" 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_5b028af8-09d8-47e2-9bdb-41e198892cc5" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9cd80fea-5dfb-4221-84f1-b169848f56e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingLiabilitiesMember_a57dad68-b7e3-490e-aefa-a0bb1fa6989f" xlink:href="upst-20230331.xsd#upst_LoanServicingLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9cd80fea-5dfb-4221-84f1-b169848f56e5" xlink:to="loc_upst_LoanServicingLiabilitiesMember_a57dad68-b7e3-490e-aefa-a0bb1fa6989f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingRollforwardDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementLoanServicingRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementLoanServicingRollforwardDetails" xlink:type="extended" id="i813d24517f064ebebab747cb18cc9f83_FairValueMeasurementLoanServicingRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetsAtFairValueLineItems_5a3666ea-8d91-4016-b382-a2106e0277e7" 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_13fea2e8-2770-499e-b1b9-ea8e634cbade" 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_5a3666ea-8d91-4016-b382-a2106e0277e7" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_13fea2e8-2770-499e-b1b9-ea8e634cbade" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_6caf59c5-c866-4c04-81c7-c90a35eb2d17" 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_13fea2e8-2770-499e-b1b9-ea8e634cbade" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_6caf59c5-c866-4c04-81c7-c90a35eb2d17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAdditions_076dcad1-232b-4128-b904-5df9574095e8" 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_13fea2e8-2770-499e-b1b9-ea8e634cbade" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAdditions_076dcad1-232b-4128-b904-5df9574095e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingAssetAtFairValueGainLossIncludedInEarnings_4eedd320-6036-45d5-911c-febb058fe2d5" xlink:href="upst-20230331.xsd#upst_ServicingAssetAtFairValueGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingAssetAtFairValueAmountRollForward_13fea2e8-2770-499e-b1b9-ea8e634cbade" xlink:to="loc_upst_ServicingAssetAtFairValueGainLossIncludedInEarnings_4eedd320-6036-45d5-911c-febb058fe2d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_51076345-ce71-4c9f-93dc-3c9371603694" 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_d1e5771c-940f-4b16-a3a0-be4b79a8fd25" 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_5a3666ea-8d91-4016-b382-a2106e0277e7" xlink:to="loc_us-gaap_ServicingAssetsAtFairValueTable_d1e5771c-940f-4b16-a3a0-be4b79a8fd25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_3d200254-4e1d-42bb-8f02-78e0ef6b7a97" 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_d1e5771c-940f-4b16-a3a0-be4b79a8fd25" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_3d200254-4e1d-42bb-8f02-78e0ef6b7a97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3d200254-4e1d-42bb-8f02-78e0ef6b7a97_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_3d200254-4e1d-42bb-8f02-78e0ef6b7a97" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3d200254-4e1d-42bb-8f02-78e0ef6b7a97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a81a9017-1333-438e-b1d2-544363c6f0e6" 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_3d200254-4e1d-42bb-8f02-78e0ef6b7a97" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a81a9017-1333-438e-b1d2-544363c6f0e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingAssetsMember_7182f9da-497e-4243-8248-0e1b9c5a3ee0" xlink:href="upst-20230331.xsd#upst_LoanServicingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a81a9017-1333-438e-b1d2-544363c6f0e6" xlink:to="loc_upst_LoanServicingAssetsMember_7182f9da-497e-4243-8248-0e1b9c5a3ee0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1abe7638-1a2c-486f-b3da-21a4df2275f2" 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_d1e5771c-940f-4b16-a3a0-be4b79a8fd25" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1abe7638-1a2c-486f-b3da-21a4df2275f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1abe7638-1a2c-486f-b3da-21a4df2275f2_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_1abe7638-1a2c-486f-b3da-21a4df2275f2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1abe7638-1a2c-486f-b3da-21a4df2275f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c121ff3d-1e8e-4d80-8a61-1f07b4595ee0" 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_1abe7638-1a2c-486f-b3da-21a4df2275f2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c121ff3d-1e8e-4d80-8a61-1f07b4595ee0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_994ebb7d-b3a4-4abf-a532-2c675d41bdd7" 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_c121ff3d-1e8e-4d80-8a61-1f07b4595ee0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_994ebb7d-b3a4-4abf-a532-2c675d41bdd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilitiesAtFairValueLineItems_46e7b0b7-8ad7-4f32-a687-e22ddc0c985a" 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_fba69561-a299-4455-b20f-1ccda25ce79d" 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_46e7b0b7-8ad7-4f32-a687-e22ddc0c985a" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_fba69561-a299-4455-b20f-1ccda25ce79d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_d7bd6618-aa74-4d95-bb4f-fac21f1a6d43" 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_fba69561-a299-4455-b20f-1ccda25ce79d" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAmount_d7bd6618-aa74-4d95-bb4f-fac21f1a6d43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAdditions_0932d432-b380-4752-8151-d0bdad1dcff6" 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_fba69561-a299-4455-b20f-1ccda25ce79d" xlink:to="loc_us-gaap_ServicingLiabilityAtFairValueAdditions_0932d432-b380-4752-8151-d0bdad1dcff6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings_b413f3ea-633d-4c1e-8b05-6919574ef3cb" xlink:href="upst-20230331.xsd#upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServicingLiabilityAtFairValueAmountRollForward_fba69561-a299-4455-b20f-1ccda25ce79d" xlink:to="loc_upst_ServicingLiabilityAtFairValueGainLossIncludedInEarnings_b413f3ea-633d-4c1e-8b05-6919574ef3cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingLiabilityAtFairValueAmount_68aff92a-e1b9-47aa-8043-e89b904b28e2" 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_9f33ade5-d445-48ec-b1c2-17645bedea1c" 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_46e7b0b7-8ad7-4f32-a687-e22ddc0c985a" xlink:to="loc_us-gaap_ServicingLiabilitiesAtFairValueTable_9f33ade5-d445-48ec-b1c2-17645bedea1c" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cb61d7b-fa16-41cd-bddf-26c1ae342a4b" 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_9f33ade5-d445-48ec-b1c2-17645bedea1c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_9cb61d7b-fa16-41cd-bddf-26c1ae342a4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9cb61d7b-fa16-41cd-bddf-26c1ae342a4b_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_da2e2959-d034-4448-ac99-9e74f67cc23d" 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_a480d085-df6c-4eee-b3f7-3aaf61e767d0" 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_746f72b4-dc10-4d79-94c5-f83e0be30385" 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_9f33ade5-d445-48ec-b1c2-17645bedea1c" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_746f72b4-dc10-4d79-94c5-f83e0be30385" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_746f72b4-dc10-4d79-94c5-f83e0be30385_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_746f72b4-dc10-4d79-94c5-f83e0be30385" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_746f72b4-dc10-4d79-94c5-f83e0be30385_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_02d91774-c6a0-487b-b5a7-c56384ede206" 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_746f72b4-dc10-4d79-94c5-f83e0be30385" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_02d91774-c6a0-487b-b5a7-c56384ede206" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LoanServicingLiabilitiesMember_b962b732-c555-48b9-b2bb-305d5d65ab48" xlink:href="upst-20230331.xsd#upst_LoanServicingLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_02d91774-c6a0-487b-b5a7-c56384ede206" xlink:to="loc_upst_LoanServicingLiabilitiesMember_b962b732-c555-48b9-b2bb-305d5d65ab48" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/FairValueMeasurementTrailingFeeRollforwardDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#FairValueMeasurementTrailingFeeRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/FairValueMeasurementTrailingFeeRollforwardDetails" xlink:type="extended" id="i320a9d77de2b4ca18bcaa2a01f9fbd5c_FairValueMeasurementTrailingFeeRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_bc1a6cc1-54f3-4b1a-b59e-86228ea605e4" 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_67cea87a-b4bc-47b5-81b7-36773e1ca689" 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_bc1a6cc1-54f3-4b1a-b59e-86228ea605e4" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_67cea87a-b4bc-47b5-81b7-36773e1ca689" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_f6bf9005-4e2b-4b27-a1c1-68525baf618e" 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_67cea87a-b4bc-47b5-81b7-36773e1ca689" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_f6bf9005-4e2b-4b27-a1c1-68525baf618e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_b820aaf4-981a-450b-9776-2df7e290be52" 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_67cea87a-b4bc-47b5-81b7-36773e1ca689" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_b820aaf4-981a-450b-9776-2df7e290be52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_efcc8135-b1c5-4d68-8d59-fbe7320d8b5d" 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_67cea87a-b4bc-47b5-81b7-36773e1ca689" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_efcc8135-b1c5-4d68-8d59-fbe7320d8b5d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_eeb760b9-8566-4722-b8e7-b24c443d890f" 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_67cea87a-b4bc-47b5-81b7-36773e1ca689" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_eeb760b9-8566-4722-b8e7-b24c443d890f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_46a6b219-2549-40c7-a999-df890641d7ae" 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_82a042b0-c5bf-4c24-b943-165af730d075" 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_bc1a6cc1-54f3-4b1a-b59e-86228ea605e4" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_82a042b0-c5bf-4c24-b943-165af730d075" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6ade5bb8-521f-4067-a8cd-13964c10701e" 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_82a042b0-c5bf-4c24-b943-165af730d075" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6ade5bb8-521f-4067-a8cd-13964c10701e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6ade5bb8-521f-4067-a8cd-13964c10701e_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_6ade5bb8-521f-4067-a8cd-13964c10701e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6ade5bb8-521f-4067-a8cd-13964c10701e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_dcfb548b-545a-433d-9e06-aaeae2124bbe" 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_6ade5bb8-521f-4067-a8cd-13964c10701e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_dcfb548b-545a-433d-9e06-aaeae2124bbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_94bcd8fd-cee9-4c17-821e-da20c6c4327e" 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_dcfb548b-545a-433d-9e06-aaeae2124bbe" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_94bcd8fd-cee9-4c17-821e-da20c6c4327e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_c12ba78e-e728-4323-9fc9-a15d0a3eee56" 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_82a042b0-c5bf-4c24-b943-165af730d075" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_c12ba78e-e728-4323-9fc9-a15d0a3eee56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_c12ba78e-e728-4323-9fc9-a15d0a3eee56_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_c12ba78e-e728-4323-9fc9-a15d0a3eee56" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_c12ba78e-e728-4323-9fc9-a15d0a3eee56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f23c74c6-fdae-4b0c-a3eb-91f874b42b7d" 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_c12ba78e-e728-4323-9fc9-a15d0a3eee56" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f23c74c6-fdae-4b0c-a3eb-91f874b42b7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TrailingFeeLiabilitiesMember_76a20e19-0d8c-4a14-b918-2881290f3405" xlink:href="upst-20230331.xsd#upst_TrailingFeeLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f23c74c6-fdae-4b0c-a3eb-91f874b42b7d" xlink:to="loc_upst_TrailingFeeLiabilitiesMember_76a20e19-0d8c-4a14-b918-2881290f3405" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="extended" id="i483002030acf41f1a9402dc6cafbb0b9_GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d01f7743-7ada-498b-b3f9-4e56044b00a4" 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_35c02a86-7284-40e7-9f69-feffef5258df" 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_d01f7743-7ada-498b-b3f9-4e56044b00a4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_35c02a86-7284-40e7-9f69-feffef5258df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_b563383c-8a12-4be9-9048-d6e147f10ca7" 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_d01f7743-7ada-498b-b3f9-4e56044b00a4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_b563383c-8a12-4be9-9048-d6e147f10ca7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8d184fac-3f77-4f5e-916e-5669aac07fe1" 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_d01f7743-7ada-498b-b3f9-4e56044b00a4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8d184fac-3f77-4f5e-916e-5669aac07fe1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_53873723-e938-4835-a28d-8f17955edda0" 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_d01f7743-7ada-498b-b3f9-4e56044b00a4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_53873723-e938-4835-a28d-8f17955edda0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2241ee26-b831-4e73-a825-a87aa7a17d10" 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_d01f7743-7ada-498b-b3f9-4e56044b00a4" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2241ee26-b831-4e73-a825-a87aa7a17d10" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ce435da0-c53d-4aff-a3d0-42fff3f3907f" 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_2241ee26-b831-4e73-a825-a87aa7a17d10" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ce435da0-c53d-4aff-a3d0-42fff3f3907f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ce435da0-c53d-4aff-a3d0-42fff3f3907f_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_ce435da0-c53d-4aff-a3d0-42fff3f3907f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ce435da0-c53d-4aff-a3d0-42fff3f3907f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_14d3a5eb-23b1-49f6-bbb5-69f087b8e259" 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_ce435da0-c53d-4aff-a3d0-42fff3f3907f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_14d3a5eb-23b1-49f6-bbb5-69f087b8e259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_b99431f2-a823-458c-8185-28baf30b2d2b" 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_14d3a5eb-23b1-49f6-bbb5-69f087b8e259" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_b99431f2-a823-458c-8185-28baf30b2d2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_f6bd06df-357d-42f7-be9d-83c9564d6dd1" 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_14d3a5eb-23b1-49f6-bbb5-69f087b8e259" xlink:to="loc_us-gaap_CustomerRelationshipsMember_f6bd06df-357d-42f7-be9d-83c9564d6dd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_bf0329e0-b11d-40ba-90ed-fc35a9861393" 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_2241ee26-b831-4e73-a825-a87aa7a17d10" xlink:to="loc_srt_RangeAxis_bf0329e0-b11d-40ba-90ed-fc35a9861393" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bf0329e0-b11d-40ba-90ed-fc35a9861393_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_bf0329e0-b11d-40ba-90ed-fc35a9861393" xlink:to="loc_srt_RangeMember_bf0329e0-b11d-40ba-90ed-fc35a9861393_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_86d699fe-0684-41c6-9337-eb7ea2a4bf75" 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_bf0329e0-b11d-40ba-90ed-fc35a9861393" xlink:to="loc_srt_RangeMember_86d699fe-0684-41c6-9337-eb7ea2a4bf75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_f6ff64e6-4311-4ade-aceb-e5763f4e2e57" 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_86d699fe-0684-41c6-9337-eb7ea2a4bf75" xlink:to="loc_srt_WeightedAverageMember_f6ff64e6-4311-4ade-aceb-e5763f4e2e57" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BalanceSheetComponentsPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#BalanceSheetComponentsPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BalanceSheetComponentsPropertyPlantandEquipmentDetails" xlink:type="extended" id="i21109f665d0c4161a6d2e2f1e1277de9_BalanceSheetComponentsPropertyPlantandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_2b83b6de-e4fe-4056-9508-0f39ea4b11b1" 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_dcfac159-2ef1-497e-80db-0a1addb695ef" 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_2b83b6de-e4fe-4056-9508-0f39ea4b11b1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_dcfac159-2ef1-497e-80db-0a1addb695ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_d94b1e09-12cc-4c8a-8d0d-ccc3ee85f3fe" 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_2b83b6de-e4fe-4056-9508-0f39ea4b11b1" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_d94b1e09-12cc-4c8a-8d0d-ccc3ee85f3fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_ccca52bc-f591-4a80-8ac8-fe2a79d34a2a" 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_2b83b6de-e4fe-4056-9508-0f39ea4b11b1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_ccca52bc-f591-4a80-8ac8-fe2a79d34a2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_467a615c-88d3-48ae-be79-c82d1e4580d6" 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_2b83b6de-e4fe-4056-9508-0f39ea4b11b1" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_467a615c-88d3-48ae-be79-c82d1e4580d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3" 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_467a615c-88d3-48ae-be79-c82d1e4580d6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3_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_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b73b571e-f74c-424a-876b-46116eb8e35c" 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_fc4dfbd7-ff61-4d60-b75c-156d24f48ce3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b73b571e-f74c-424a-876b-46116eb8e35c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_e493fafe-995c-4cbf-87c0-ae0be23b177e" 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_b73b571e-f74c-424a-876b-46116eb8e35c" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_e493fafe-995c-4cbf-87c0-ae0be23b177e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_026c001c-b4b2-4df6-ae60-8e7fcc7b911b" 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_b73b571e-f74c-424a-876b-46116eb8e35c" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_026c001c-b4b2-4df6-ae60-8e7fcc7b911b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_66de3c5f-5efa-44e3-9e0f-8f757aa9dfcc" 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_b73b571e-f74c-424a-876b-46116eb8e35c" xlink:to="loc_us-gaap_ComputerEquipmentMember_66de3c5f-5efa-44e3-9e0f-8f757aa9dfcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_1d8ca145-d964-405c-8fea-a0a96252c00b" 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_b73b571e-f74c-424a-876b-46116eb8e35c" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_1d8ca145-d964-405c-8fea-a0a96252c00b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#BalanceSheetComponentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="extended" id="ie6a303c5d33e4178a609d4b103bdd6a8_BalanceSheetComponentsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_42ed957a-4776-4566-b356-238d355ae3e7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_0f91a8e5-3afd-40f7-98ad-f3ac588700e9" 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_RestructuringCostAndReserveLineItems_42ed957a-4776-4566-b356-238d355ae3e7" xlink:to="loc_us-gaap_Depreciation_0f91a8e5-3afd-40f7-98ad-f3ac588700e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareNet_05be8ed1-2dca-424d-89d6-8617ed33fa48" 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_RestructuringCostAndReserveLineItems_42ed957a-4776-4566-b356-238d355ae3e7" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareNet_05be8ed1-2dca-424d-89d6-8617ed33fa48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_2e5875c7-4d70-4bba-a8bd-5367bee6ea7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_42ed957a-4776-4566-b356-238d355ae3e7" xlink:to="loc_us-gaap_RestructuringCharges_2e5875c7-4d70-4bba-a8bd-5367bee6ea7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d63679f4-c151-42d7-9719-f39c75b2b432" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_42ed957a-4776-4566-b356-238d355ae3e7" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d63679f4-c151-42d7-9719-f39c75b2b432" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_39439129-439c-43d0-85af-3e3aec62ee54" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d63679f4-c151-42d7-9719-f39c75b2b432" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_39439129-439c-43d0-85af-3e3aec62ee54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_39439129-439c-43d0-85af-3e3aec62ee54_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_39439129-439c-43d0-85af-3e3aec62ee54" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_39439129-439c-43d0-85af-3e3aec62ee54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_a8536e3d-b753-4c35-8a9f-a2ff4386e8a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_39439129-439c-43d0-85af-3e3aec62ee54" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_a8536e3d-b753-4c35-8a9f-a2ff4386e8a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ImpairmentOfIntangibleAssetsMember_5715cfbd-61e3-45d8-ad4c-289876dbfff5" xlink:href="upst-20230331.xsd#upst_ImpairmentOfIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_a8536e3d-b753-4c35-8a9f-a2ff4386e8a5" xlink:to="loc_upst_ImpairmentOfIntangibleAssetsMember_5715cfbd-61e3-45d8-ad4c-289876dbfff5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d63679f4-c151-42d7-9719-f39c75b2b432" xlink:to="loc_us-gaap_RestructuringPlanAxis_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a" xlink:to="loc_us-gaap_RestructuringPlanDomain_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_97ea7923-0698-4f44-836d-7f88c7f40f80" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_69b4d0f1-c9a0-4cc7-b076-2c28ce4f5d6a" xlink:to="loc_us-gaap_RestructuringPlanDomain_97ea7923-0698-4f44-836d-7f88c7f40f80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_January2023PlanMember_8fb485ef-8b39-462d-a7a8-136cbf05c0ff" xlink:href="upst-20230331.xsd#upst_January2023PlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_97ea7923-0698-4f44-836d-7f88c7f40f80" xlink:to="loc_upst_January2023PlanMember_8fb485ef-8b39-462d-a7a8-136cbf05c0ff" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsScheduleofaggregateprincipaloutstandingofallloansDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#BorrowingsScheduleofaggregateprincipaloutstandingofallloansDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsScheduleofaggregateprincipaloutstandingofallloansDetails" xlink:type="extended" id="ie815b14161d4436fb5d66b1f480f4862_BorrowingsScheduleofaggregateprincipaloutstandingofallloansDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_c4ec2b51-dbc2-497f-af8b-584dd0e98014" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LongTermAndShortTermDebtGross_bf339a10-f9f8-484d-9229-8e2ff6cf6008" xlink:href="upst-20230331.xsd#upst_LongTermAndShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_c4ec2b51-dbc2-497f-af8b-584dd0e98014" xlink:to="loc_upst_LongTermAndShortTermDebtGross_bf339a10-f9f8-484d-9229-8e2ff6cf6008" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_e827aee0-94b3-4c67-a452-b629208f9ce6" 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_c4ec2b51-dbc2-497f-af8b-584dd0e98014" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_e827aee0-94b3-4c67-a452-b629208f9ce6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_7a0048e7-df9f-4540-99df-55a415be2072" 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_c4ec2b51-dbc2-497f-af8b-584dd0e98014" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_7a0048e7-df9f-4540-99df-55a415be2072" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_5f8ee8a9-d831-4998-84cc-d4627f914cc5" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_c4ec2b51-dbc2-497f-af8b-584dd0e98014" xlink:to="loc_upst_ScheduleOfBorrowingsTable_5f8ee8a9-d831-4998-84cc-d4627f914cc5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e" 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_5f8ee8a9-d831-4998-84cc-d4627f914cc5" xlink:to="loc_us-gaap_DebtInstrumentAxis_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e_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_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_aa6940e2-3ff7-4293-b356-679d5af10d36" 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_a471a34b-6027-4d48-9f3f-0a0cb4a49d1e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_aa6940e2-3ff7-4293-b356-679d5af10d36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_WarehouseCreditFacilityMember_258a87c3-e37f-4b83-ba5a-557e591afc3b" xlink:href="upst-20230331.xsd#upst_WarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_aa6940e2-3ff7-4293-b356-679d5af10d36" xlink:to="loc_upst_WarehouseCreditFacilityMember_258a87c3-e37f-4b83-ba5a-557e591afc3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TwentyTwentySixNotesMember_329d75d2-7312-4836-8ea1-74ba593cd53a" xlink:href="upst-20230331.xsd#upst_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_aa6940e2-3ff7-4293-b356-679d5af10d36" xlink:to="loc_upst_TwentyTwentySixNotesMember_329d75d2-7312-4836-8ea1-74ba593cd53a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_73109f73-049c-4f0c-adb9-24836d2979a3" 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_5f8ee8a9-d831-4998-84cc-d4627f914cc5" xlink:to="loc_us-gaap_CreditFacilityAxis_73109f73-049c-4f0c-adb9-24836d2979a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_73109f73-049c-4f0c-adb9-24836d2979a3_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_73109f73-049c-4f0c-adb9-24836d2979a3" xlink:to="loc_us-gaap_CreditFacilityDomain_73109f73-049c-4f0c-adb9-24836d2979a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0b9e1ca6-f113-4834-a67b-f8a7c99e0b62" 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_73109f73-049c-4f0c-adb9-24836d2979a3" xlink:to="loc_us-gaap_CreditFacilityDomain_0b9e1ca6-f113-4834-a67b-f8a7c99e0b62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_ce75bfce-5687-49e5-9a2c-a1bf20fa25fe" 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_0b9e1ca6-f113-4834-a67b-f8a7c99e0b62" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_ce75bfce-5687-49e5-9a2c-a1bf20fa25fe" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#BorrowingsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsNarrativeDetails" xlink:type="extended" id="ib94534ed8b0440589448cff99b9bcaef_BorrowingsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_12edc5be-8490-4410-8e9d-bda393e43a6e" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_12edc5be-8490-4410-8e9d-bda393e43a6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_26022f93-bbce-4e71-9f14-0954cda8929e" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_26022f93-bbce-4e71-9f14-0954cda8929e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_ffcad86c-15f2-4815-a503-e1c775b2d2f9" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_ffcad86c-15f2-4815-a503-e1c775b2d2f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_67509ce5-4090-4ebb-b0e9-cd81ae7ca13a" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_67509ce5-4090-4ebb-b0e9-cd81ae7ca13a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LineOfCreditFacilityMaximumAdvanceRate_22b56b62-7803-4f11-9c33-7ffd22b46991" xlink:href="upst-20230331.xsd#upst_LineOfCreditFacilityMaximumAdvanceRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_LineOfCreditFacilityMaximumAdvanceRate_22b56b62-7803-4f11-9c33-7ffd22b46991" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentMaximumAdvanceRatePercentOfOutstandingPrincipalHeld_b7930ace-06cd-45fb-97e3-3c28a62d0b57" xlink:href="upst-20230331.xsd#upst_DebtInstrumentMaximumAdvanceRatePercentOfOutstandingPrincipalHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentMaximumAdvanceRatePercentOfOutstandingPrincipalHeld_b7930ace-06cd-45fb-97e3-3c28a62d0b57" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_e1cf66d7-2ec6-40a3-b263-9ddabcee0604" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_e1cf66d7-2ec6-40a3-b263-9ddabcee0604" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_45814989-8bf6-4260-8c83-a3c45755e470" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_45814989-8bf6-4260-8c83-a3c45755e470" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentAdditionalAggregatePrincipal_221c7c87-02fe-4b69-aa59-a4f4591dcbd0" xlink:href="upst-20230331.xsd#upst_DebtInstrumentAdditionalAggregatePrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentAdditionalAggregatePrincipal_221c7c87-02fe-4b69-aa59-a4f4591dcbd0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_e37c14df-b8b8-4993-a5e9-2ddfbf897bfa" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_e37c14df-b8b8-4993-a5e9-2ddfbf897bfa" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_61030a73-f5df-44c4-b206-bad43235378e" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_61030a73-f5df-44c4-b206-bad43235378e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_642ae287-7616-4b83-aff3-80f721139eb9" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_642ae287-7616-4b83-aff3-80f721139eb9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_033e1cd9-497d-4ee1-af40-1d93e8443535" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_033e1cd9-497d-4ee1-af40-1d93e8443535" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_624e09c4-e94b-4581-b7a7-56aae186ff0a" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_624e09c4-e94b-4581-b7a7-56aae186ff0a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_66e42334-2daa-4120-95f2-30434cc3a815" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_66e42334-2daa-4120-95f2-30434cc3a815" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_42d6ef8d-cf0b-4c38-b7e0-36d157facee9" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_42d6ef8d-cf0b-4c38-b7e0-36d157facee9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate_b659d5f3-be03-4d95-9dbd-1c7ffb3a787e" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentConvertibleMaximumPercentageOfProductOfLastReportedSalePriceAndConversionRate_b659d5f3-be03-4d95-9dbd-1c7ffb3a787e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_2d415e76-5b2a-4ad8-966b-c482d988b526" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_2d415e76-5b2a-4ad8-966b-c482d988b526" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_a43d0c58-57a4-40e7-bd40-f1312a697732" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_a43d0c58-57a4-40e7-bd40-f1312a697732" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_c6eb637b-1d19-4211-ba8e-557397595dc3" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_c6eb637b-1d19-4211-ba8e-557397595dc3" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_bf2c2c3a-c503-47c0-963f-0eeee49b2560" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_bf2c2c3a-c503-47c0-963f-0eeee49b2560" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayable_29aa9001-bfe7-4382-baee-5824ff3f47cd" 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_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_us-gaap_ConvertibleNotesPayable_29aa9001-bfe7-4382-baee-5824ff3f47cd" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PaymentsForCappedCalls_32f94544-2dbf-4052-b325-dfbef135dba8" xlink:href="upst-20230331.xsd#upst_PaymentsForCappedCalls"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_PaymentsForCappedCalls_32f94544-2dbf-4052-b325-dfbef135dba8" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice_f9f8a025-39fa-4af2-ba72-30b5717326b8" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsInitialStrikePrice_f9f8a025-39fa-4af2-ba72-30b5717326b8" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice_ac2c7755-9df0-46de-9be2-fe6c553aab85" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsInitialCapPrice_ac2c7755-9df0-46de-9be2-fe6c553aab85" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered_2717f320-d5ae-4d3f-b095-62a45850c6e2" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_DebtInstrumentConvertibleCappedCallsNumberOfSharesOfCommonStockCovered_2717f320-d5ae-4d3f-b095-62a45850c6e2" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_97aabbc5-2c0c-44e7-93a6-6ce7292ee53b" xlink:to="loc_upst_ScheduleOfBorrowingsTable_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_90bda2fa-5bcd-425d-bff9-5cb6095136c8" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_us-gaap_VariableRateAxis_90bda2fa-5bcd-425d-bff9-5cb6095136c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_90bda2fa-5bcd-425d-bff9-5cb6095136c8_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_90bda2fa-5bcd-425d-bff9-5cb6095136c8" xlink:to="loc_us-gaap_VariableRateDomain_90bda2fa-5bcd-425d-bff9-5cb6095136c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_efa04e83-3c4a-404f-9270-c56acb301008" 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_90bda2fa-5bcd-425d-bff9-5cb6095136c8" xlink:to="loc_us-gaap_VariableRateDomain_efa04e83-3c4a-404f-9270-c56acb301008" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_42d7eee4-ae62-434e-a6e5-d2a72e4153bf" 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_efa04e83-3c4a-404f-9270-c56acb301008" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_42d7eee4-ae62-434e-a6e5-d2a72e4153bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember_4c76fbdc-6672-4023-9013-869688ecfced" xlink:href="upst-20230331.xsd#upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_efa04e83-3c4a-404f-9270-c56acb301008" xlink:to="loc_upst_WeightedAverageCostOfCommercialPaperNotesIssuedByTheLenderMember_4c76fbdc-6672-4023-9013-869688ecfced" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTBenchmarkRateMember_44f47419-8ec9-4d66-9fa9-a0529a361103" xlink:href="upst-20230331.xsd#upst_UAWTBenchmarkRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_efa04e83-3c4a-404f-9270-c56acb301008" xlink:to="loc_upst_UAWTBenchmarkRateMember_44f47419-8ec9-4d66-9fa9-a0529a361103" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_43442084-25f6-49e6-a95f-809bf08d2989" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_us-gaap_DebtInstrumentAxis_43442084-25f6-49e6-a95f-809bf08d2989" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_43442084-25f6-49e6-a95f-809bf08d2989_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_43442084-25f6-49e6-a95f-809bf08d2989" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_43442084-25f6-49e6-a95f-809bf08d2989_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_06891ecd-207f-4f0f-a2b7-aa7eb6a81a5f" 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_43442084-25f6-49e6-a95f-809bf08d2989" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_06891ecd-207f-4f0f-a2b7-aa7eb6a81a5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityMember_7dec8a65-d343-49e1-b733-1dcc3c546d9a" xlink:href="upst-20230331.xsd#upst_ULTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_06891ecd-207f-4f0f-a2b7-aa7eb6a81a5f" xlink:to="loc_upst_ULTWarehouseCreditFacilityMember_7dec8a65-d343-49e1-b733-1dcc3c546d9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityCommittedMember_6c47c3e5-a41b-4288-984e-35d292cee3e8" xlink:href="upst-20230331.xsd#upst_ULTWarehouseCreditFacilityCommittedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ULTWarehouseCreditFacilityMember_7dec8a65-d343-49e1-b733-1dcc3c546d9a" xlink:to="loc_upst_ULTWarehouseCreditFacilityCommittedMember_6c47c3e5-a41b-4288-984e-35d292cee3e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityUncommittedMember_fb897b68-2a23-4f56-8dbe-0acd089996fe" xlink:href="upst-20230331.xsd#upst_ULTWarehouseCreditFacilityUncommittedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ULTWarehouseCreditFacilityMember_7dec8a65-d343-49e1-b733-1dcc3c546d9a" xlink:to="loc_upst_ULTWarehouseCreditFacilityUncommittedMember_fb897b68-2a23-4f56-8dbe-0acd089996fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTWarehouseCreditFacilityMember_b1237764-187c-4ac6-8389-835a447c3aad" xlink:href="upst-20230331.xsd#upst_UAWTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_06891ecd-207f-4f0f-a2b7-aa7eb6a81a5f" xlink:to="loc_upst_UAWTWarehouseCreditFacilityMember_b1237764-187c-4ac6-8389-835a447c3aad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_TwentyTwentySixNotesMember_0ecf8270-ae4f-4bbd-8ca2-3e41461e8a4e" xlink:href="upst-20230331.xsd#upst_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_06891ecd-207f-4f0f-a2b7-aa7eb6a81a5f" xlink:to="loc_upst_TwentyTwentySixNotesMember_0ecf8270-ae4f-4bbd-8ca2-3e41461e8a4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_71242ad0-c8e4-4f17-943a-c563099b67e3" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_srt_RangeAxis_71242ad0-c8e4-4f17-943a-c563099b67e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_71242ad0-c8e4-4f17-943a-c563099b67e3_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_71242ad0-c8e4-4f17-943a-c563099b67e3" xlink:to="loc_srt_RangeMember_71242ad0-c8e4-4f17-943a-c563099b67e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fdb19816-dd02-41b3-b0ea-e8d863175733" 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_71242ad0-c8e4-4f17-943a-c563099b67e3" xlink:to="loc_srt_RangeMember_fdb19816-dd02-41b3-b0ea-e8d863175733" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_71c24d61-8ea0-487e-9862-36f723a8e718" 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_fdb19816-dd02-41b3-b0ea-e8d863175733" xlink:to="loc_srt_MinimumMember_71c24d61-8ea0-487e-9862-36f723a8e718" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_b54136b3-9a62-4a28-b474-6c119d1a3291" 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_fdb19816-dd02-41b3-b0ea-e8d863175733" xlink:to="loc_srt_MaximumMember_b54136b3-9a62-4a28-b474-6c119d1a3291" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_5f80793c-15f4-417d-9342-f618239d9ed6" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_us-gaap_CreditFacilityAxis_5f80793c-15f4-417d-9342-f618239d9ed6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5f80793c-15f4-417d-9342-f618239d9ed6_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_5f80793c-15f4-417d-9342-f618239d9ed6" xlink:to="loc_us-gaap_CreditFacilityDomain_5f80793c-15f4-417d-9342-f618239d9ed6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_4a22b170-7f81-4884-8c3a-4fd46d6b5f3c" 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_5f80793c-15f4-417d-9342-f618239d9ed6" xlink:to="loc_us-gaap_CreditFacilityDomain_4a22b170-7f81-4884-8c3a-4fd46d6b5f3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_043d56d6-7667-4928-8259-a463d0c31a85" 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_4a22b170-7f81-4884-8c3a-4fd46d6b5f3c" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_043d56d6-7667-4928-8259-a463d0c31a85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_46f68cb4-0028-4cb4-84b6-294a72731ea4" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_46f68cb4-0028-4cb4-84b6-294a72731ea4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_46f68cb4-0028-4cb4-84b6-294a72731ea4_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_46f68cb4-0028-4cb4-84b6-294a72731ea4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_46f68cb4-0028-4cb4-84b6-294a72731ea4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_acd80b3e-0f64-4b52-b01d-63c792e78204" 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_46f68cb4-0028-4cb4-84b6-294a72731ea4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_acd80b3e-0f64-4b52-b01d-63c792e78204" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_36cb1e5a-758e-4c77-9278-47a9a34e464e" 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_acd80b3e-0f64-4b52-b01d-63c792e78204" xlink:to="loc_us-gaap_ConvertibleDebtMember_36cb1e5a-758e-4c77-9278-47a9a34e464e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionAxis_cd8ed82a-aa85-4408-871c-244a3afe9c00" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConversionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_upst_ScheduleOfBorrowingsTable_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_upst_DebtInstrumentConversionAxis_cd8ed82a-aa85-4408-871c-244a3afe9c00" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionDomain_cd8ed82a-aa85-4408-871c-244a3afe9c00_default" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_upst_DebtInstrumentConversionAxis_cd8ed82a-aa85-4408-871c-244a3afe9c00" xlink:to="loc_upst_DebtInstrumentConversionDomain_cd8ed82a-aa85-4408-871c-244a3afe9c00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_DebtInstrumentConversionDomain_f8eb2def-3e69-4fe4-8604-c659aafdc20f" xlink:href="upst-20230331.xsd#upst_DebtInstrumentConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_upst_DebtInstrumentConversionAxis_cd8ed82a-aa85-4408-871c-244a3afe9c00" xlink:to="loc_upst_DebtInstrumentConversionDomain_f8eb2def-3e69-4fe4-8604-c659aafdc20f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodOneMember_5c13e5c2-7a9c-4519-842d-6b9da978f950" xlink:href="upst-20230331.xsd#upst_ConversionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_f8eb2def-3e69-4fe4-8604-c659aafdc20f" xlink:to="loc_upst_ConversionPeriodOneMember_5c13e5c2-7a9c-4519-842d-6b9da978f950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodTwoMember_6fa0a6c2-41d0-4064-9eef-f94ddfd3ceb2" xlink:href="upst-20230331.xsd#upst_ConversionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_f8eb2def-3e69-4fe4-8604-c659aafdc20f" xlink:to="loc_upst_ConversionPeriodTwoMember_6fa0a6c2-41d0-4064-9eef-f94ddfd3ceb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ConversionPeriodThreeMember_e1ee6717-61e7-4856-8308-bc1ccd04864a" xlink:href="upst-20230331.xsd#upst_ConversionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_DebtInstrumentConversionDomain_f8eb2def-3e69-4fe4-8604-c659aafdc20f" xlink:to="loc_upst_ConversionPeriodThreeMember_e1ee6717-61e7-4856-8308-bc1ccd04864a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd_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_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_2d4e968b-de27-47f2-985c-aa054b404dac" 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_a2720e6d-37e7-4161-99c6-f4ee2aa8aebd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_2d4e968b-de27-47f2-985c-aa054b404dac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PrimaryBeneficiaryMember_73f15ad0-adb3-4b77-8baa-75473b7f1671" xlink:href="upst-20230331.xsd#upst_PrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_2d4e968b-de27-47f2-985c-aa054b404dac" xlink:to="loc_upst_PrimaryBeneficiaryMember_73f15ad0-adb3-4b77-8baa-75473b7f1671" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_43d5f6ae-9cd7-46ed-9f79-29521737098a" 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_6caaf4dd-3639-4de8-8bed-09c4b0f756bb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_43d5f6ae-9cd7-46ed-9f79-29521737098a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_43d5f6ae-9cd7-46ed-9f79-29521737098a_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_43d5f6ae-9cd7-46ed-9f79-29521737098a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_43d5f6ae-9cd7-46ed-9f79-29521737098a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_160bcbd1-1b1a-4cfd-bda6-d9d13696b231" 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_43d5f6ae-9cd7-46ed-9f79-29521737098a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_160bcbd1-1b1a-4cfd-bda6-d9d13696b231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_f4f23896-290a-4059-871d-88390eccee20" 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_160bcbd1-1b1a-4cfd-bda6-d9d13696b231" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_f4f23896-290a-4059-871d-88390eccee20" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/BorrowingsAssetsPledgedasCollateralDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#BorrowingsAssetsPledgedasCollateralDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/BorrowingsAssetsPledgedasCollateralDetails" xlink:type="extended" id="i0d17711a9bad482e848bbcc44ac79a3f_BorrowingsAssetsPledgedasCollateralDetails">
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsLineItems_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_LongTermAndShortTermDebtGross_09197b6e-3a1c-4259-86b4-3445c041dd48" xlink:href="upst-20230331.xsd#upst_LongTermAndShortTermDebtGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:to="loc_upst_LongTermAndShortTermDebtGross_09197b6e-3a1c-4259-86b4-3445c041dd48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableGross_06c69e15-2823-4588-b3e0-66a0c5323df4" 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_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:to="loc_us-gaap_NotesReceivableGross_06c69e15-2823-4588-b3e0-66a0c5323df4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_aaee59be-a67e-4bb0-84d0-69569e98edcc" 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_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_aaee59be-a67e-4bb0-84d0-69569e98edcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_ea22eaa9-8af6-40f8-a928-1ae56f93b6a9" 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_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:to="loc_us-gaap_RestrictedCash_ea22eaa9-8af6-40f8-a928-1ae56f93b6a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ScheduleOfBorrowingsTable_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:href="upst-20230331.xsd#upst_ScheduleOfBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_upst_ScheduleOfBorrowingsLineItems_5c3cfd5b-9cdf-448d-b083-036a97223bd0" xlink:to="loc_upst_ScheduleOfBorrowingsTable_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_a1ae27a0-20a9-47f2-997b-33bedecec38e" 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_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:to="loc_us-gaap_DebtInstrumentAxis_a1ae27a0-20a9-47f2-997b-33bedecec38e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a1ae27a0-20a9-47f2-997b-33bedecec38e_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_a1ae27a0-20a9-47f2-997b-33bedecec38e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a1ae27a0-20a9-47f2-997b-33bedecec38e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_5f748a58-24b8-477e-95ac-33bb0de58216" 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_a1ae27a0-20a9-47f2-997b-33bedecec38e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_5f748a58-24b8-477e-95ac-33bb0de58216" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ULTWarehouseCreditFacilityMember_ea438790-e790-4382-9759-3d6def04da2d" xlink:href="upst-20230331.xsd#upst_ULTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5f748a58-24b8-477e-95ac-33bb0de58216" xlink:to="loc_upst_ULTWarehouseCreditFacilityMember_ea438790-e790-4382-9759-3d6def04da2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UAWTWarehouseCreditFacilityMember_ba59b8c3-0439-4646-80b1-f98cf2698504" xlink:href="upst-20230331.xsd#upst_UAWTWarehouseCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5f748a58-24b8-477e-95ac-33bb0de58216" xlink:to="loc_upst_UAWTWarehouseCreditFacilityMember_ba59b8c3-0439-4646-80b1-f98cf2698504" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ba60ad0a-3f6d-4af3-9ec7-5ce495614639" 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_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:to="loc_us-gaap_CreditFacilityAxis_ba60ad0a-3f6d-4af3-9ec7-5ce495614639" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ba60ad0a-3f6d-4af3-9ec7-5ce495614639_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_ba60ad0a-3f6d-4af3-9ec7-5ce495614639" xlink:to="loc_us-gaap_CreditFacilityDomain_ba60ad0a-3f6d-4af3-9ec7-5ce495614639_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d0d7e606-7d01-4c7b-a281-895dae8ce180" 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_ba60ad0a-3f6d-4af3-9ec7-5ce495614639" xlink:to="loc_us-gaap_CreditFacilityDomain_d0d7e606-7d01-4c7b-a281-895dae8ce180" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_cfdd3af9-e4b5-4d2d-b07c-a506ccf45070" 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_d0d7e606-7d01-4c7b-a281-895dae8ce180" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_cfdd3af9-e4b5-4d2d-b07c-a506ccf45070" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f" 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_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f_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_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_92646228-6c1b-491d-a9bd-5cd4a051c717" 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_1c3ad5cd-bdd6-46c6-997c-9cf2f65ee09f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_92646228-6c1b-491d-a9bd-5cd4a051c717" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_85ba5bae-faf2-4e4e-8df9-a09e08bafa84" 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_92646228-6c1b-491d-a9bd-5cd4a051c717" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_85ba5bae-faf2-4e4e-8df9-a09e08bafa84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusAxis_affa7175-1275-4d36-8d95-1e8eaa3871ac" 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_cbbaea05-8998-4bde-a8b7-abf47125340a" xlink:to="loc_us-gaap_PledgedStatusAxis_affa7175-1275-4d36-8d95-1e8eaa3871ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_affa7175-1275-4d36-8d95-1e8eaa3871ac_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_affa7175-1275-4d36-8d95-1e8eaa3871ac" xlink:to="loc_us-gaap_PledgedStatusDomain_affa7175-1275-4d36-8d95-1e8eaa3871ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_54f6274e-cdff-4108-ba17-8dcd0bd6d2d5" 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_affa7175-1275-4d36-8d95-1e8eaa3871ac" xlink:to="loc_us-gaap_PledgedStatusDomain_54f6274e-cdff-4108-ba17-8dcd0bd6d2d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetPledgedAsCollateralMember_431207d6-495c-4a14-b35d-a2da3a2a1b37" 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_54f6274e-cdff-4108-ba17-8dcd0bd6d2d5" xlink:to="loc_us-gaap_AssetPledgedAsCollateralMember_431207d6-495c-4a14-b35d-a2da3a2a1b37" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityReservedSharesofCommonStockforIssuanceDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityReservedSharesofCommonStockforIssuanceDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityReservedSharesofCommonStockforIssuanceDetails" xlink:type="extended" id="ib83dddd6bf80491285fccadd3fb696c5_StockholdersEquityReservedSharesofCommonStockforIssuanceDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_4694db73-4773-485e-8f44-86984efb4f78" 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_c6e17cba-f205-45fa-9e34-76370fee63f4" 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_4694db73-4773-485e-8f44-86984efb4f78" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_c6e17cba-f205-45fa-9e34-76370fee63f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_fc986aad-184c-403c-bd18-9ec27ecdd84d" 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_4694db73-4773-485e-8f44-86984efb4f78" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_fc986aad-184c-403c-bd18-9ec27ecdd84d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b2715e14-8103-4f97-a647-b396258ba81a" 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_fc986aad-184c-403c-bd18-9ec27ecdd84d" xlink:to="loc_us-gaap_AwardTypeAxis_b2715e14-8103-4f97-a647-b396258ba81a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b2715e14-8103-4f97-a647-b396258ba81a_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_b2715e14-8103-4f97-a647-b396258ba81a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b2715e14-8103-4f97-a647-b396258ba81a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_52aa00ac-a035-43ff-81cc-9213af73d35a" 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_b2715e14-8103-4f97-a647-b396258ba81a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_52aa00ac-a035-43ff-81cc-9213af73d35a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4f3b4719-9b30-445d-a6a4-69fad2a49d36" 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_52aa00ac-a035-43ff-81cc-9213af73d35a" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4f3b4719-9b30-445d-a6a4-69fad2a49d36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_dc394c8a-9b25-400d-ad9e-8df0ee43cef8" 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_52aa00ac-a035-43ff-81cc-9213af73d35a" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_dc394c8a-9b25-400d-ad9e-8df0ee43cef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_5dd5b577-26b2-4292-9f7e-f1de2be53e15" 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_52aa00ac-a035-43ff-81cc-9213af73d35a" xlink:to="loc_us-gaap_PerformanceSharesMember_5dd5b577-26b2-4292-9f7e-f1de2be53e15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_131957e4-8ff2-4c20-979e-eb853683ca49" 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_52aa00ac-a035-43ff-81cc-9213af73d35a" xlink:to="loc_us-gaap_EmployeeStockMember_131957e4-8ff2-4c20-979e-eb853683ca49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_3603fc35-020a-44a8-b10d-aa58b25e1f63" 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_fc986aad-184c-403c-bd18-9ec27ecdd84d" xlink:to="loc_us-gaap_PlanNameAxis_3603fc35-020a-44a8-b10d-aa58b25e1f63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_3603fc35-020a-44a8-b10d-aa58b25e1f63_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_3603fc35-020a-44a8-b10d-aa58b25e1f63" xlink:to="loc_us-gaap_PlanNameDomain_3603fc35-020a-44a8-b10d-aa58b25e1f63_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_a3dedefa-3ec8-4915-8e15-47b87944a81e" 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_3603fc35-020a-44a8-b10d-aa58b25e1f63" xlink:to="loc_us-gaap_PlanNameDomain_a3dedefa-3ec8-4915-8e15-47b87944a81e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_A2020EquityIncentivePlanMember_04bf883d-685b-48c3-97cd-b5b31125aa23" xlink:href="upst-20230331.xsd#upst_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_a3dedefa-3ec8-4915-8e15-47b87944a81e" xlink:to="loc_upst_A2020EquityIncentivePlanMember_04bf883d-685b-48c3-97cd-b5b31125aa23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ae57630c-2790-47fb-a1aa-4a073248e950" 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_fc986aad-184c-403c-bd18-9ec27ecdd84d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ae57630c-2790-47fb-a1aa-4a073248e950" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ae57630c-2790-47fb-a1aa-4a073248e950_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_ae57630c-2790-47fb-a1aa-4a073248e950" xlink:to="loc_us-gaap_ClassOfStockDomain_ae57630c-2790-47fb-a1aa-4a073248e950_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5b9c5d6e-8dc7-4c89-96fc-bf04adb02015" 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_ae57630c-2790-47fb-a1aa-4a073248e950" xlink:to="loc_us-gaap_ClassOfStockDomain_5b9c5d6e-8dc7-4c89-96fc-bf04adb02015" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_6bc17941-1877-4dec-8dbc-a93a104c8648" 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_5b9c5d6e-8dc7-4c89-96fc-bf04adb02015" xlink:to="loc_us-gaap_CommonClassAMember_6bc17941-1877-4dec-8dbc-a93a104c8648" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityNarrativeDetails" xlink:type="extended" id="if1cee73ac5d341209871d326e0f68525_StockholdersEquityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" 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_c739700b-2eee-457b-b73f-db168adb5f93" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_c739700b-2eee-457b-b73f-db168adb5f93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_1e1b18ea-df9f-40af-8eb7-1f5a3110f5f8" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_1e1b18ea-df9f-40af-8eb7-1f5a3110f5f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_401f1c1a-ec5d-4fa5-82a0-6d2049da1bb9" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_401f1c1a-ec5d-4fa5-82a0-6d2049da1bb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_a05d53bd-5dde-4e0e-8841-7ddf4dabaa92" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_a05d53bd-5dde-4e0e-8841-7ddf4dabaa92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9b6eaf83-b2b0-444e-8220-b9fe10e1aa38" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9b6eaf83-b2b0-444e-8220-b9fe10e1aa38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_e60750c1-b0f3-4f3d-82ca-c2bb859d2273" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_e60750c1-b0f3-4f3d-82ca-c2bb859d2273" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f89526d1-265c-4c08-a3b8-e5af41252bd4" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f89526d1-265c-4c08-a3b8-e5af41252bd4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_2ee7d394-3868-4a1f-aa2d-12f20eb0721b" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_2ee7d394-3868-4a1f-aa2d-12f20eb0721b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_d1693dbe-5610-4051-a7a5-6bea7d3ac406" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_d1693dbe-5610-4051-a7a5-6bea7d3ac406" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_2fe62a59-d98e-4011-991d-0f15a5d30d2e" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_2fe62a59-d98e-4011-991d-0f15a5d30d2e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1513f749-1259-44fd-a280-af966793c282" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1513f749-1259-44fd-a280-af966793c282" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_c5078e46-4b2d-461c-bb37-df69febf0dcb" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_c5078e46-4b2d-461c-bb37-df69febf0dcb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_f42cb99b-ba7c-4ab1-b3b3-87ed50659fe8" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_f42cb99b-ba7c-4ab1-b3b3-87ed50659fe8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementAwardsCancelledSettlementInShares_59eb959f-ca0d-4fd5-b3f9-0df882b77571" xlink:href="upst-20230331.xsd#upst_ShareBasedCompensationArrangementAwardsCancelledSettlementInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_upst_ShareBasedCompensationArrangementAwardsCancelledSettlementInShares_59eb959f-ca0d-4fd5-b3f9-0df882b77571" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_AnnualTargetBonusOpportunityPercentageOfSalaryPercent_85b46ba0-f31e-4813-adc9-48388dd82e99" xlink:href="upst-20230331.xsd#upst_AnnualTargetBonusOpportunityPercentageOfSalaryPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_upst_AnnualTargetBonusOpportunityPercentageOfSalaryPercent_85b46ba0-f31e-4813-adc9-48388dd82e99" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfVestingTranches_d91cf3bf-927d-4aeb-8d18-cfc54b7c4ab8" xlink:href="upst-20230331.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfVestingTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfVestingTranches_d91cf3bf-927d-4aeb-8d18-cfc54b7c4ab8" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b43f1425-ba69-40f0-ae6b-33fdbca90047" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b43f1425-ba69-40f0-ae6b-33fdbca90047" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_2b3454ba-3b8f-4ab7-96ac-62b65033a80e" xlink:href="upst-20230331.xsd#upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_upst_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_2b3454ba-3b8f-4ab7-96ac-62b65033a80e" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4a02507d-7f0b-41fe-b3f9-10df1b156a78" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4a02507d-7f0b-41fe-b3f9-10df1b156a78" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_958c8295-75ab-482a-badc-50cbdace0ab3" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_958c8295-75ab-482a-badc-50cbdace0ab3" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_1547a39b-b212-47f9-a389-8f512228c8b0" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_1547a39b-b212-47f9-a389-8f512228c8b0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_127b43a5-44b1-41f7-985a-0b2ed5ace924" 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_789ed633-8285-4149-bb5a-40ad838bd9bd" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_7082a6cb-e79a-4885-9084-5fde8b06148b" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_us-gaap_AwardTypeAxis_7082a6cb-e79a-4885-9084-5fde8b06148b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7082a6cb-e79a-4885-9084-5fde8b06148b_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_7082a6cb-e79a-4885-9084-5fde8b06148b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7082a6cb-e79a-4885-9084-5fde8b06148b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f9b66f1e-3289-4b36-91af-fb9cdc40274e" 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_7082a6cb-e79a-4885-9084-5fde8b06148b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7218e96e-7628-4857-9188-a90ade38d527" 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_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7218e96e-7628-4857-9188-a90ade38d527" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_e49aa3e7-0691-42f8-82f8-9f9d97f16830" 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_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_e49aa3e7-0691-42f8-82f8-9f9d97f16830" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_4d101aef-613f-4d8a-8055-3b17b770f446" 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_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:to="loc_us-gaap_RestrictedStockMember_4d101aef-613f-4d8a-8055-3b17b770f446" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_3a4794ce-4db6-4b6c-9a17-aae23eca0b0b" 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_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:to="loc_us-gaap_PerformanceSharesMember_3a4794ce-4db6-4b6c-9a17-aae23eca0b0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_7904448a-192d-40eb-9698-36f58dd335a3" 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_f9b66f1e-3289-4b36-91af-fb9cdc40274e" xlink:to="loc_us-gaap_EmployeeStockMember_7904448a-192d-40eb-9698-36f58dd335a3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_d1df4300-bf87-4bca-9dc7-767e20a3e35e" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_us-gaap_PlanNameAxis_d1df4300-bf87-4bca-9dc7-767e20a3e35e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_d1df4300-bf87-4bca-9dc7-767e20a3e35e_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_d1df4300-bf87-4bca-9dc7-767e20a3e35e" xlink:to="loc_us-gaap_PlanNameDomain_d1df4300-bf87-4bca-9dc7-767e20a3e35e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_861846c2-58d9-4beb-b175-ff604d69b484" 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_d1df4300-bf87-4bca-9dc7-767e20a3e35e" xlink:to="loc_us-gaap_PlanNameDomain_861846c2-58d9-4beb-b175-ff604d69b484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_A2020EquityIncentivePlanMember_6c201846-74b0-4409-abf6-d5f01edd7072" xlink:href="upst-20230331.xsd#upst_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_861846c2-58d9-4beb-b175-ff604d69b484" xlink:to="loc_upst_A2020EquityIncentivePlanMember_6c201846-74b0-4409-abf6-d5f01edd7072" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_70f5f30f-5301-4a5c-ac47-4977504308e1" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_us-gaap_StatementClassOfStockAxis_70f5f30f-5301-4a5c-ac47-4977504308e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_70f5f30f-5301-4a5c-ac47-4977504308e1_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_70f5f30f-5301-4a5c-ac47-4977504308e1" xlink:to="loc_us-gaap_ClassOfStockDomain_70f5f30f-5301-4a5c-ac47-4977504308e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0280a2eb-1347-494f-be8f-c227a7443da9" 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_70f5f30f-5301-4a5c-ac47-4977504308e1" xlink:to="loc_us-gaap_ClassOfStockDomain_0280a2eb-1347-494f-be8f-c227a7443da9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_22bdfc39-ceb2-4f0a-a45c-d4cb0a93f943" 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_0280a2eb-1347-494f-be8f-c227a7443da9" xlink:to="loc_us-gaap_CommonClassAMember_22bdfc39-ceb2-4f0a-a45c-d4cb0a93f943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b1175e22-27b4-431f-9530-adb6ccd8eae2" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_srt_RangeAxis_b1175e22-27b4-431f-9530-adb6ccd8eae2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b1175e22-27b4-431f-9530-adb6ccd8eae2_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_b1175e22-27b4-431f-9530-adb6ccd8eae2" xlink:to="loc_srt_RangeMember_b1175e22-27b4-431f-9530-adb6ccd8eae2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d6a0cf2f-b7d5-462b-af94-dd1b752a9d94" 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_b1175e22-27b4-431f-9530-adb6ccd8eae2" xlink:to="loc_srt_RangeMember_d6a0cf2f-b7d5-462b-af94-dd1b752a9d94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_81d57de9-1bad-4460-8df3-44eac60142b4" 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_d6a0cf2f-b7d5-462b-af94-dd1b752a9d94" xlink:to="loc_srt_WeightedAverageMember_81d57de9-1bad-4460-8df3-44eac60142b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a02ba8be-7fdb-44b4-8ab8-11b5c2a0704b" 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_d6a0cf2f-b7d5-462b-af94-dd1b752a9d94" xlink:to="loc_srt_MinimumMember_a02ba8be-7fdb-44b4-8ab8-11b5c2a0704b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c741600b-711e-4844-af86-44c76c948443" 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_d6a0cf2f-b7d5-462b-af94-dd1b752a9d94" xlink:to="loc_srt_MaximumMember_c741600b-711e-4844-af86-44c76c948443" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_6610a907-e9ac-4b10-9d62-0f0fd29d9d28" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_6610a907-e9ac-4b10-9d62-0f0fd29d9d28" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6610a907-e9ac-4b10-9d62-0f0fd29d9d28_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_6610a907-e9ac-4b10-9d62-0f0fd29d9d28" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6610a907-e9ac-4b10-9d62-0f0fd29d9d28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5e09b831-db3d-4d2a-975a-731402eec14d" 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_6610a907-e9ac-4b10-9d62-0f0fd29d9d28" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5e09b831-db3d-4d2a-975a-731402eec14d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ProdigySoftwareIncMember_f6ffff07-ac14-4b64-9c78-34cb50b09d2f" xlink:href="upst-20230331.xsd#upst_ProdigySoftwareIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5e09b831-db3d-4d2a-975a-731402eec14d" xlink:to="loc_upst_ProdigySoftwareIncMember_f6ffff07-ac14-4b64-9c78-34cb50b09d2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_982da288-7448-4ad7-b9f4-008979126027" 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_127b43a5-44b1-41f7-985a-0b2ed5ace924" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_982da288-7448-4ad7-b9f4-008979126027" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_982da288-7448-4ad7-b9f4-008979126027_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_982da288-7448-4ad7-b9f4-008979126027" xlink:to="loc_us-gaap_EquityComponentDomain_982da288-7448-4ad7-b9f4-008979126027_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f0cc12e9-9a5b-4875-8ce0-a1ec1ac71aaa" 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_982da288-7448-4ad7-b9f4-008979126027" xlink:to="loc_us-gaap_EquityComponentDomain_f0cc12e9-9a5b-4875-8ce0-a1ec1ac71aaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_b9e324f4-e78f-41ad-aa16-ca276e043371" 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_f0cc12e9-9a5b-4875-8ce0-a1ec1ac71aaa" xlink:to="loc_us-gaap_CommonStockMember_b9e324f4-e78f-41ad-aa16-ca276e043371" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityRSUActivityDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityRSUActivityDetails" xlink:type="extended" id="i4115cbbf7e4b46018b451f11f5e786ff_StockholdersEquityRSUActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_31e03a7b-fbf6-4822-845d-b463307e192b" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_31e03a7b-fbf6-4822-845d-b463307e192b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2af9c611-9c0a-42d8-8884-5225fc4e8f2d" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2af9c611-9c0a-42d8-8884-5225fc4e8f2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_2d488538-9c88-42f7-9ef5-19dc342ceab3" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_2d488538-9c88-42f7-9ef5-19dc342ceab3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_f1e26354-cc5f-4575-8cc5-9155cacfc9fb" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_f1e26354-cc5f-4575-8cc5-9155cacfc9fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2d5c457b-4904-466e-a616-bab4dcc3f36c" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_ddcd0abe-ea7a-4f02-afbd-d539ede1bd1e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2d5c457b-4904-466e-a616-bab4dcc3f36c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c069002f-f036-4571-bbb5-8e433f6edec5" 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_9853a25d-c0e6-4e61-8ee1-950965a62eeb" 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_31e03a7b-fbf6-4822-845d-b463307e192b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_9853a25d-c0e6-4e61-8ee1-950965a62eeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_4065a33e-a777-4167-86f3-828fb72f944b" 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_9853a25d-c0e6-4e61-8ee1-950965a62eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_4065a33e-a777-4167-86f3-828fb72f944b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4416a11b-e5e2-436d-9ae4-33463dac262d" 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_9853a25d-c0e6-4e61-8ee1-950965a62eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4416a11b-e5e2-436d-9ae4-33463dac262d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_bc04d6aa-c5cc-472f-a644-d9d275db6a1f" 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_9853a25d-c0e6-4e61-8ee1-950965a62eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_bc04d6aa-c5cc-472f-a644-d9d275db6a1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_5104da6d-37c0-4195-8634-12b7b276943a" 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_9853a25d-c0e6-4e61-8ee1-950965a62eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_5104da6d-37c0-4195-8634-12b7b276943a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_96d32006-f322-4d0e-b13f-b486537f09c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_279583d5-1233-4885-999b-1bce67176436" 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_31e03a7b-fbf6-4822-845d-b463307e192b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_279583d5-1233-4885-999b-1bce67176436" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb" 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_279583d5-1233-4885-999b-1bce67176436" xlink:to="loc_us-gaap_AwardTypeAxis_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb_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_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_75dff6f1-b109-4d43-b277-171bb4c28d9c" 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_207cdf7d-0b5e-4dac-89c9-864f3c9b6cbb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_75dff6f1-b109-4d43-b277-171bb4c28d9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0070602b-e825-46e3-86fa-9d966a5b62e6" 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_75dff6f1-b109-4d43-b277-171bb4c28d9c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0070602b-e825-46e3-86fa-9d966a5b62e6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityRestrictedStockActivityDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityRestrictedStockActivityDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityRestrictedStockActivityDetails" xlink:type="extended" id="i0af43820cc8a4e699bb249358a975730_StockholdersEquityRestrictedStockActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b10f9a29-9b23-4440-aadc-2675a9ac348f" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_6b2ac778-b13b-4c6f-bd6c-4d796945f644" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b10f9a29-9b23-4440-aadc-2675a9ac348f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_6b2ac778-b13b-4c6f-bd6c-4d796945f644" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3d7fd9e3-dbbe-4023-bf72-9a14f0023322" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_6b2ac778-b13b-4c6f-bd6c-4d796945f644" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3d7fd9e3-dbbe-4023-bf72-9a14f0023322" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_adcf60a3-77e1-42d6-bef8-ab9de2157966" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_6b2ac778-b13b-4c6f-bd6c-4d796945f644" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_adcf60a3-77e1-42d6-bef8-ab9de2157966" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e37378fc-d837-4cbb-b9ed-4594b622a6a8" 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_924a54cf-b327-4162-88ff-772e0e592127" 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_b10f9a29-9b23-4440-aadc-2675a9ac348f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_924a54cf-b327-4162-88ff-772e0e592127" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_27fde8c1-92d2-43fa-a4db-5bafcd83a51b" 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_924a54cf-b327-4162-88ff-772e0e592127" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_27fde8c1-92d2-43fa-a4db-5bafcd83a51b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_f8421dd0-da03-4dd7-874d-daebe3975e1b" 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_924a54cf-b327-4162-88ff-772e0e592127" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_f8421dd0-da03-4dd7-874d-daebe3975e1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_1a477b37-f8b2-40a8-afbd-29853707afe5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0fe6b365-1bec-4621-9a68-41a7b64ca136" 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_b10f9a29-9b23-4440-aadc-2675a9ac348f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0fe6b365-1bec-4621-9a68-41a7b64ca136" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b4fb49f0-0b8d-4643-aa1e-db846d61c453" 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_0fe6b365-1bec-4621-9a68-41a7b64ca136" xlink:to="loc_us-gaap_AwardTypeAxis_b4fb49f0-0b8d-4643-aa1e-db846d61c453" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b4fb49f0-0b8d-4643-aa1e-db846d61c453_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_b4fb49f0-0b8d-4643-aa1e-db846d61c453" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b4fb49f0-0b8d-4643-aa1e-db846d61c453_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_71b47971-e061-4ad7-8797-ea50930dde03" 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_b4fb49f0-0b8d-4643-aa1e-db846d61c453" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_71b47971-e061-4ad7-8797-ea50930dde03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_28c67bf2-7a07-44a5-aa67-acfc47dea1dc" 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_71b47971-e061-4ad7-8797-ea50930dde03" xlink:to="loc_us-gaap_RestrictedStockMember_28c67bf2-7a07-44a5-aa67-acfc47dea1dc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityWeightedAverageAssumptionsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityWeightedAverageAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityWeightedAverageAssumptionsDetails" xlink:type="extended" id="i3d4b8b8ae9724d8db15ef8e80179447f_StockholdersEquityWeightedAverageAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cbf33e2b-a7b4-4030-827c-40ee911ce24d" 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_979a74dc-8d5a-4cfc-899d-117ded22add8" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_979a74dc-8d5a-4cfc-899d-117ded22add8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_105ed006-e333-4341-9064-c5b5191fc93f" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_105ed006-e333-4341-9064-c5b5191fc93f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_ab1c0415-3522-4458-badc-fd6d7602751e" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_ab1c0415-3522-4458-badc-fd6d7602751e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_8b020e3e-3a75-46df-95a7-7462ab6c4088" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_8b020e3e-3a75-46df-95a7-7462ab6c4088" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_684af1af-6063-4de9-93a2-a4405e749455" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_684af1af-6063-4de9-93a2-a4405e749455" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a7df1aa4-22db-47fa-9af6-658385736065" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a7df1aa4-22db-47fa-9af6-658385736065" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_f178c8d1-16d1-458a-baf0-ec980a24b349" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_f178c8d1-16d1-458a-baf0-ec980a24b349" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_d188351f-988c-4d7d-930c-ca49ab445644" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_d188351f-988c-4d7d-930c-ca49ab445644" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8d21606f-6463-4c2c-9259-e6a6c73aef5e" 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_cbf33e2b-a7b4-4030-827c-40ee911ce24d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8d21606f-6463-4c2c-9259-e6a6c73aef5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f007297e-a316-4c0e-a002-23f56cec0c15" 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_8d21606f-6463-4c2c-9259-e6a6c73aef5e" xlink:to="loc_us-gaap_AwardTypeAxis_f007297e-a316-4c0e-a002-23f56cec0c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f007297e-a316-4c0e-a002-23f56cec0c15_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_f007297e-a316-4c0e-a002-23f56cec0c15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f007297e-a316-4c0e-a002-23f56cec0c15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_384fa186-b9a5-4dfb-bf3a-98fde91f4c8d" 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_f007297e-a316-4c0e-a002-23f56cec0c15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_384fa186-b9a5-4dfb-bf3a-98fde91f4c8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_3122ee3c-a21b-410b-9e0d-75b42d7e3a4f" 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_384fa186-b9a5-4dfb-bf3a-98fde91f4c8d" xlink:to="loc_us-gaap_EmployeeStockOptionMember_3122ee3c-a21b-410b-9e0d-75b42d7e3a4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_e39d0fe3-a3c7-43f5-9f1f-be0bc9d65645" 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_384fa186-b9a5-4dfb-bf3a-98fde91f4c8d" xlink:to="loc_us-gaap_PerformanceSharesMember_e39d0fe3-a3c7-43f5-9f1f-be0bc9d65645" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_8d715f34-cd7f-42c2-ad2a-a71a72e9eddd" 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_384fa186-b9a5-4dfb-bf3a-98fde91f4c8d" xlink:to="loc_us-gaap_EmployeeStockMember_8d715f34-cd7f-42c2-ad2a-a71a72e9eddd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_840f7112-b90d-4334-9edc-c7bb868ade00" 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_8d21606f-6463-4c2c-9259-e6a6c73aef5e" xlink:to="loc_srt_RangeAxis_840f7112-b90d-4334-9edc-c7bb868ade00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_840f7112-b90d-4334-9edc-c7bb868ade00_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_840f7112-b90d-4334-9edc-c7bb868ade00" xlink:to="loc_srt_RangeMember_840f7112-b90d-4334-9edc-c7bb868ade00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3d82e5eb-2ac8-43ae-bcbb-59c41646cbf9" 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_840f7112-b90d-4334-9edc-c7bb868ade00" xlink:to="loc_srt_RangeMember_3d82e5eb-2ac8-43ae-bcbb-59c41646cbf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_2e07c783-117e-4f79-b57c-0feb0b497a63" 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_3d82e5eb-2ac8-43ae-bcbb-59c41646cbf9" xlink:to="loc_srt_MinimumMember_2e07c783-117e-4f79-b57c-0feb0b497a63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c82a3e4a-0e33-47c7-8bfc-50c7969634d2" 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_3d82e5eb-2ac8-43ae-bcbb-59c41646cbf9" xlink:to="loc_srt_MaximumMember_c82a3e4a-0e33-47c7-8bfc-50c7969634d2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/StockholdersEquityExpenseDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#StockholdersEquityExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/StockholdersEquityExpenseDetails" xlink:type="extended" id="i98dc5fd97878437a89a59c439016eb43_StockholdersEquityExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_f577be27-4ea8-4d32-80f8-f354e4b3625a" 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_b3cda8af-cf5c-49ea-b9aa-2d31af84d946" 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_f577be27-4ea8-4d32-80f8-f354e4b3625a" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_b3cda8af-cf5c-49ea-b9aa-2d31af84d946" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0e877ff4-cba7-45a6-a234-453edf423977" 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_f577be27-4ea8-4d32-80f8-f354e4b3625a" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0e877ff4-cba7-45a6-a234-453edf423977" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_c8bee80b-f176-403c-b3db-7271c1e9b60c" 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_0e877ff4-cba7-45a6-a234-453edf423977" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_c8bee80b-f176-403c-b3db-7271c1e9b60c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c8bee80b-f176-403c-b3db-7271c1e9b60c_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_c8bee80b-f176-403c-b3db-7271c1e9b60c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c8bee80b-f176-403c-b3db-7271c1e9b60c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_e3e068c3-baba-4fa9-871b-50ed95c36a41" 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_c8bee80b-f176-403c-b3db-7271c1e9b60c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_e3e068c3-baba-4fa9-871b-50ed95c36a41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_4d910d89-fa1a-456d-9e9e-b6cb4a28be2b" 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_e3e068c3-baba-4fa9-871b-50ed95c36a41" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_4d910d89-fa1a-456d-9e9e-b6cb4a28be2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_CustomerOperationsMember_ce8513cc-aa8e-40f2-8636-0a87b535c52a" xlink:href="upst-20230331.xsd#upst_CustomerOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_e3e068c3-baba-4fa9-871b-50ed95c36a41" xlink:to="loc_upst_CustomerOperationsMember_ce8513cc-aa8e-40f2-8636-0a87b535c52a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_EngineeringAndProductDevelopmentMember_681dea93-3426-4464-8364-b606d4d38d0e" xlink:href="upst-20230331.xsd#upst_EngineeringAndProductDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_e3e068c3-baba-4fa9-871b-50ed95c36a41" xlink:to="loc_upst_EngineeringAndProductDevelopmentMember_681dea93-3426-4464-8364-b606d4d38d0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_311f8ee1-370c-4715-bf6c-9811735a73a0" 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_e3e068c3-baba-4fa9-871b-50ed95c36a41" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_311f8ee1-370c-4715-bf6c-9811735a73a0" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="id937900b2a954e0abb452aa52caf3098_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_66a2ed4d-f3ca-43ce-932b-bca6e0e33e42" 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_b886f9e4-5bda-4e16-a3c6-8e9c569d5772" 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_66a2ed4d-f3ca-43ce-932b-bca6e0e33e42" xlink:to="loc_us-gaap_PurchaseObligation_b886f9e4-5bda-4e16-a3c6-8e9c569d5772" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_ef955708-a7b3-4c73-b28f-c1b6f6023a22" 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_66a2ed4d-f3ca-43ce-932b-bca6e0e33e42" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_ef955708-a7b3-4c73-b28f-c1b6f6023a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_6bc49960-fa79-4263-b3b6-93838ea52a79" 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_66a2ed4d-f3ca-43ce-932b-bca6e0e33e42" xlink:to="loc_us-gaap_LossContingenciesTable_6bc49960-fa79-4263-b3b6-93838ea52a79" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_baad18fe-26f0-42d5-b41a-8f70bf464cf3" 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_6bc49960-fa79-4263-b3b6-93838ea52a79" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_baad18fe-26f0-42d5-b41a-8f70bf464cf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_baad18fe-26f0-42d5-b41a-8f70bf464cf3_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_baad18fe-26f0-42d5-b41a-8f70bf464cf3" xlink:to="loc_us-gaap_LossContingencyNatureDomain_baad18fe-26f0-42d5-b41a-8f70bf464cf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_dfbf8ee7-e950-4d27-8d4a-bbf4ae4c692a" 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_baad18fe-26f0-42d5-b41a-8f70bf464cf3" xlink:to="loc_us-gaap_LossContingencyNatureDomain_dfbf8ee7-e950-4d27-8d4a-bbf4ae4c692a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ObligationToRepurchaseReceivablesSoldMember_a74705b8-d02d-4161-8d03-7938f040916d" 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_dfbf8ee7-e950-4d27-8d4a-bbf4ae4c692a" xlink:to="loc_us-gaap_ObligationToRepurchaseReceivablesSoldMember_a74705b8-d02d-4161-8d03-7938f040916d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/NetIncomeLossPerShareAttributabletoUpstartHoldingsIncCommonStockholdersAntidilutiveSecuritiesDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#NetIncomeLossPerShareAttributabletoUpstartHoldingsIncCommonStockholdersAntidilutiveSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/NetIncomeLossPerShareAttributabletoUpstartHoldingsIncCommonStockholdersAntidilutiveSecuritiesDetails" xlink:type="extended" id="i6bebca4a32e44089b0e48e28aacdb59e_NetIncomeLossPerShareAttributabletoUpstartHoldingsIncCommonStockholdersAntidilutiveSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_acb0fc8f-40ae-47af-96e2-26f2815073e1" 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_b6400b56-cca1-42f6-bc12-a83a88c0cc88" 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_acb0fc8f-40ae-47af-96e2-26f2815073e1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b6400b56-cca1-42f6-bc12-a83a88c0cc88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5a02cfaf-e1ad-4d29-be8d-46683e686dda" 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_acb0fc8f-40ae-47af-96e2-26f2815073e1" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5a02cfaf-e1ad-4d29-be8d-46683e686dda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_612be9eb-41dc-49b2-8863-1d297206750c" 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_5a02cfaf-e1ad-4d29-be8d-46683e686dda" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_612be9eb-41dc-49b2-8863-1d297206750c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_612be9eb-41dc-49b2-8863-1d297206750c_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_612be9eb-41dc-49b2-8863-1d297206750c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_612be9eb-41dc-49b2-8863-1d297206750c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_0e4addca-d3ec-4e72-9f85-4583c46b9581" 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_612be9eb-41dc-49b2-8863-1d297206750c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_12b3256c-130d-4cba-a418-aeccea84080b" 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_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:to="loc_us-gaap_EmployeeStockOptionMember_12b3256c-130d-4cba-a418-aeccea84080b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_60c1399c-afd7-4b88-8ff4-760439d5a091" 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_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_60c1399c-afd7-4b88-8ff4-760439d5a091" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_PerformanceRestrictedStockUnitsPRSUsMember_71f87dfa-2754-4328-b970-766121634a4b" xlink:href="upst-20230331.xsd#upst_PerformanceRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:to="loc_upst_PerformanceRestrictedStockUnitsPRSUsMember_71f87dfa-2754-4328-b970-766121634a4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_058737d1-0d4c-407d-a47f-4b297f112b7d" 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_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:to="loc_us-gaap_EmployeeStockMember_058737d1-0d4c-407d-a47f-4b297f112b7d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_68f0d685-c693-49af-ac09-2459cdab89e6" 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_0e4addca-d3ec-4e72-9f85-4583c46b9581" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_68f0d685-c693-49af-ac09-2459cdab89e6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/ReorganizationExpensesDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#ReorganizationExpensesDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/ReorganizationExpensesDetails" xlink:type="extended" id="i3b012ea0062d48c2b410146872214e05_ReorganizationExpensesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminatedPercent_9dcd324f-e9f0-48f1-a81f-253553d4d720" xlink:href="upst-20230331.xsd#upst_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminatedPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_upst_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminatedPercent_9dcd324f-e9f0-48f1-a81f-253553d4d720" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated_2870035a-4728-47f2-a317-106a11490987" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated_2870035a-4728-47f2-a317-106a11490987" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_44a4d79d-c3b3-4ab1-9d4a-052c3f08a19a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_us-gaap_RestructuringCharges_44a4d79d-c3b3-4ab1-9d4a-052c3f08a19a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_de138354-f082-4d46-862e-fe0786afcb87" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_us-gaap_PaymentsForRestructuring_de138354-f082-4d46-862e-fe0786afcb87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_RestructuringAndRelatedCostOneTimeNonCashSavingsAmount_17df6644-9b4b-4904-a2ed-638d62348fbd" xlink:href="upst-20230331.xsd#upst_RestructuringAndRelatedCostOneTimeNonCashSavingsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_upst_RestructuringAndRelatedCostOneTimeNonCashSavingsAmount_17df6644-9b4b-4904-a2ed-638d62348fbd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_28303bc7-5340-4051-9a08-6a9b76d0b235" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e998b88c-29a9-4868-bc24-b3a5f46f4403" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_28303bc7-5340-4051-9a08-6a9b76d0b235" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_a2760532-afca-41ff-9ddc-2971a9c44eab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_28303bc7-5340-4051-9a08-6a9b76d0b235" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_a2760532-afca-41ff-9ddc-2971a9c44eab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_a2760532-afca-41ff-9ddc-2971a9c44eab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a2760532-afca-41ff-9ddc-2971a9c44eab" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_a2760532-afca-41ff-9ddc-2971a9c44eab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_47eef044-c549-4adb-93d3-1e4e7df8511d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a2760532-afca-41ff-9ddc-2971a9c44eab" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_47eef044-c549-4adb-93d3-1e4e7df8511d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_610ee76d-f931-43d9-8161-5a9ea156ccea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_47eef044-c549-4adb-93d3-1e4e7df8511d" xlink:to="loc_us-gaap_EmployeeSeveranceMember_610ee76d-f931-43d9-8161-5a9ea156ccea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_ImpairmentOfIntangibleAssetsMember_1045fa1e-d3a1-4cad-9835-f0f21d0789cd" xlink:href="upst-20230331.xsd#upst_ImpairmentOfIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_47eef044-c549-4adb-93d3-1e4e7df8511d" xlink:to="loc_upst_ImpairmentOfIntangibleAssetsMember_1045fa1e-d3a1-4cad-9835-f0f21d0789cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_7e0d8891-d520-4402-8b17-17c31668e3b8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_28303bc7-5340-4051-9a08-6a9b76d0b235" xlink:to="loc_us-gaap_RestructuringPlanAxis_7e0d8891-d520-4402-8b17-17c31668e3b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_7e0d8891-d520-4402-8b17-17c31668e3b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_7e0d8891-d520-4402-8b17-17c31668e3b8" xlink:to="loc_us-gaap_RestructuringPlanDomain_7e0d8891-d520-4402-8b17-17c31668e3b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_ee3061e0-ba4e-4030-b255-1f7ef80a0c65" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_7e0d8891-d520-4402-8b17-17c31668e3b8" xlink:to="loc_us-gaap_RestructuringPlanDomain_ee3061e0-ba4e-4030-b255-1f7ef80a0c65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_January2023PlanMember_93db0bf9-ae5e-4dbb-ab17-670edaeb0b85" xlink:href="upst-20230331.xsd#upst_January2023PlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_ee3061e0-ba4e-4030-b255-1f7ef80a0c65" xlink:to="loc_upst_January2023PlanMember_93db0bf9-ae5e-4dbb-ab17-670edaeb0b85" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.upstartholdings.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="upst-20230331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.upstartholdings.com/role/SubsequentEventsDetails" xlink:type="extended" id="i7395819428c44a1f807bf66439f6e6ce_SubsequentEventsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_0502e47d-4bd5-42e2-b951-5af1f51d7c3c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_fbf8b9fc-c055-4b05-9974-b2a27514cab7" 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_SubsequentEventLineItems_0502e47d-4bd5-42e2-b951-5af1f51d7c3c" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_fbf8b9fc-c055-4b05-9974-b2a27514cab7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_c92db18b-5841-4aa4-8bba-a367f3c9651f" 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_SubsequentEventLineItems_0502e47d-4bd5-42e2-b951-5af1f51d7c3c" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_c92db18b-5841-4aa4-8bba-a367f3c9651f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_0a07f4f9-9980-4a3c-92d0-d0757e5bf7ca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_0502e47d-4bd5-42e2-b951-5af1f51d7c3c" xlink:to="loc_us-gaap_SubsequentEventTable_0a07f4f9-9980-4a3c-92d0-d0757e5bf7ca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_0a07f4f9-9980-4a3c-92d0-d0757e5bf7ca" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_cd35de8c-bebf-4b84-9b91-e4a15ec062f0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_9bbc8d22-f812-4a07-b0a8-ad0d76a0d2dc" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_cd35de8c-bebf-4b84-9b91-e4a15ec062f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_f403567a-d2a1-4de8-841f-4e49b27f4645" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_cd35de8c-bebf-4b84-9b91-e4a15ec062f0" xlink:to="loc_us-gaap_SubsequentEventMember_f403567a-d2a1-4de8-841f-4e49b27f4645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_4b8d262a-a79d-4e98-9f65-d28cd99f3151" 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_SubsequentEventTable_0a07f4f9-9980-4a3c-92d0-d0757e5bf7ca" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_4b8d262a-a79d-4e98-9f65-d28cd99f3151" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_4b8d262a-a79d-4e98-9f65-d28cd99f3151_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_4b8d262a-a79d-4e98-9f65-d28cd99f3151" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_4b8d262a-a79d-4e98-9f65-d28cd99f3151_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1401cb2e-9a7d-4828-8eb5-6e73dc4b1445" 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_4b8d262a-a79d-4e98-9f65-d28cd99f3151" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1401cb2e-9a7d-4828-8eb5-6e73dc4b1445" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upst_UpstartPoweredPersonalLoansMember_57f96223-fc10-41e2-9197-2f042d2d1127" xlink:href="upst-20230331.xsd#upst_UpstartPoweredPersonalLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1401cb2e-9a7d-4828-8eb5-6e73dc4b1445" xlink:to="loc_upst_UpstartPoweredPersonalLoansMember_57f96223-fc10-41e2-9197-2f042d2d1127" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
