<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-10-16</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001637873</issuerCik>
        <issuerName>ACV Auctions Inc.</issuerName>
        <issuerTradingSymbol>ACVA</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001245773</rptOwnerCik>
            <rptOwnerName>JONES RENE F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O ACV AUCTIONS INC.</rptOwnerStreet1>
            <rptOwnerStreet2>640 ELLICOTT ST., SUITE 321</rptOwnerStreet2>
            <rptOwnerCity>BUFFALO</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>14203</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-10-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>46607</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.42</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2026-10-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>100000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to the Agreement and Plan of Merger, dated September 10, 2026 (the &quot;Merger Agreement&quot;), by and among ACV Auctions Inc. (&quot;ACV&quot;), Copart, Inc. (&quot;Copart&quot;), and Apple Merger Sub, Inc., a wholly owned subsidiary of Copart (&quot;Merger Sub&quot;), the shares of common stock of ACV that were tendered to Merger Sub prior to the expiration time of the offer were exchanged for $10.50 per share (&quot;Merger Consideration&quot;), net to the seller in cash, without interest, subject to any required withholding tax. After completion of the tender offer, pursuant to the terms of the Merger Agreement, Merger Sub merged with and into ACV (the &quot;Merger&quot;), with ACV surviving the Merger as a wholly owned subsidiary of Copart.</footnote>
        <footnote id="F2">Pursuant to the terms of the Merger Agreement, (i) each outstanding restricted stock unit award corresponding to shares of ACV common stock (each, an &quot;ACV RSU&quot;) held by the Reporting Person was canceled in consideration for the right to receive the Merger Consideration in respect of each share of ACV common stock then subject to the ACV RSU and (ii) each outstanding and vested option to purchase shares of ACV common stock (&quot;ACV Options&quot;) which has a per share exercise price less than the Merger Consideration was canceled in exchange for the right to receive a cash payment equal to (x) the number of shares of ACV common stock subject to such ACV Option multiplied by (y) the excess of (A) $10.50 over (B) the applicable per share exercise price of the ACV Option, subject to any required withholding taxes.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Michelle Webb, Attorney-in-Fact</signatureName>
        <signatureDate>2026-10-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
