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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-02-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001736297</issuerCik>
        <issuerName>Astera Labs, Inc.</issuerName>
        <issuerTradingSymbol>ALAB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001998053</rptOwnerCik>
            <rptOwnerName>Mohan Jitendra</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ASTERA LABS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2345 NORTH FIRST STREET</rptOwnerStreet2>
            <rptOwnerCity>SAN JOSE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95131</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Executive Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-02-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>26522</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1547710</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4689232</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Living Trust</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>699999</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>700000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 2021 Trust 1</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>700000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 2021 Trust 2</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>450001</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 2022 Trust 1</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>450001</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 2022 Trust 2</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">These shares represent an award of restricted stock units (&quot;RSUs&quot;) granted on February 6, 2026 under the Astera Labs, Inc. 2024 Stock Option and Incentive Plan. Such award provides that the RSUs shall vest as to 25% on February 15, 2027 and the remaining RSUs shall vest in 12 equal quarterly installments thereafter, subject to the Reporting Person's continuous service relationship with the Issuer through each applicable vesting date. Each RSU represents a contingent right to receive one share of the Issuer's Common Stock.</footnote>
        <footnote id="F2">These shares are owned directly by a living trust (the &quot;Living Trust&quot;), of which the Reporting Person is a trustee. The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F3">These shares are owned directly by an estate planning trust (the &quot;Trust&quot;). The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F4">These shares are owned directly by an estate planning trust (the &quot;2021 Trust 1&quot;), of which the Reporting Person is a trustee. The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F5">These shares are owned directly by an estate planning trust (the &quot;2021 Trust 2&quot;), of which the Reporting Person is a trustee. The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F6">These shares are owned directly by an estate planning trust (the &quot;2022 Trust 1&quot;). The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F7">These shares are owned directly by an estate planning trust (the &quot;2022 Trust 2&quot;). The Reporting Person disclaims beneficial ownership of these securities, except to the extent, if any, of his pecuniary interest therein, and the filing of this Form 4 is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Philip Mazzara, Attorney-in-Fact</signatureName>
        <signatureDate>2026-02-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
