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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-09-15</periodOfReport>

    <issuer>
        <issuerCik>0001836056</issuerCik>
        <issuerName>Ambrx Biopharma Inc.</issuerName>
        <issuerTradingSymbol>AMAM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001583977</rptOwnerCik>
            <rptOwnerName>Cormorant Asset Management, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 CLARENDON STREET</rptOwnerStreet1>
            <rptOwnerStreet2>52ND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02116</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001599214</rptOwnerCik>
            <rptOwnerName>Chen Bihua</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CORMORANT ASSET MANAGEMENT, LP</rptOwnerStreet1>
            <rptOwnerStreet2>200 CLARENDON STREET, 52ND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02116</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001618442</rptOwnerCik>
            <rptOwnerName>Cormorant Global Healthcare Master Fund, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 CLARENDON STREET</rptOwnerStreet1>
            <rptOwnerStreet2>52ND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02116</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001817320</rptOwnerCik>
            <rptOwnerName>Cormorant Private Healthcare Fund III LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 CLARENDON STREET</rptOwnerStreet1>
            <rptOwnerStreet2>52ND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02116</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isTenPercentOwner>true</isTenPercentOwner>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>false</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Ordinary Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2023-09-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1401505</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.0479</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>68714590</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Ordinary Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2023-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>751233</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.2447</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>69465823</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents the weighted average sale price of American Depository Shares (&quot;ADS&quot;) purchased in a series of open market transactions on the transaction date at prices ranging from $9.00 to $9.30 per ADS. The Reporting Persons undertake to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of ADS purchased at each price. All of these ADS were purchased by the Master Fund (as defined below).</footnote>
        <footnote id="F2">Information reported herein relates to ordinary shares represented by ADS owned by Cormorant Global Healthcare Master Fund, LP (the &quot;Master Fund&quot;) and Cormorant Private Healthcare Fund III, LP (&quot;Fund III&quot;). Cormorant Asset Management, LP (&quot;Cormorant&quot;) serves as the investment manager of the Master Fund and Fund III. Cormorant Global Healthcare GP, LLC (&quot;GP LLC&quot;) and Cormorant Private Healthcare GP III, LLC (&quot;GP III&quot;) serve as General Partner of the Master Fund and Fund III, respectively. Bihua Chen serves as manager of Cormorant, GP LLC and GP III. Each of the Reporting Persons disclaims beneficial ownership of the ordinary shares reported herein except to the extent of its or her pecuniary interest therein, and the filing of this Form 4 shall not be construed as an admission that any of the Reporting Persons is the beneficial owner of any such ordinary shares for purposes of Section 16(a) of the Securities Exchange Act of 1934 or for any other purpose.</footnote>
        <footnote id="F3">Represents (i) 51,172,870 ordinary shares beneficially owned by the Master Fund and (ii) 17,541,720 ordinary shares beneficially owned by Fund III.</footnote>
        <footnote id="F4">Represents (i) 51,924,103 ordinary shares beneficially owned by the Master Fund and (ii) 17,541,720 ordinary shares beneficially owned by Fund III.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ CORMORANT ASSET MANAGEMENT, LP
By: Cormorant Asset Management GP, LLC, its General Partner</signatureName>
        <signatureDate>2023-09-19</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Bihua Chen</signatureName>
        <signatureDate>2023-09-19</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ CORMORANT GLOBAL HEALTHCARE MASTER FUND, LP
By: Cormorant Global Healthcare GP, LLC, its General Partner</signatureName>
        <signatureDate>2023-09-19</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ CORMORANT PRIVATE HEALTHCARE FUND III LP
By: Cormorant Global Healthcare GP, LLC, its General Partner
By: Bihua Chen, its Manager Member</signatureName>
        <signatureDate>2023-09-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
