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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2021-05-11</periodOfReport>

    <dateOfOriginalSubmission>2021-05-18</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001500096</issuerCik>
        <issuerName>Kayne Anderson NextGen Energy &amp; Infrastructure, Inc.</issuerName>
        <issuerTradingSymbol>KMF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001645291</rptOwnerCik>
            <rptOwnerName>Mutual of Omaha Insurance Co</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3300 MUTUAL OF OMAHA PLAZA</rptOwnerStreet1>
            <rptOwnerStreet2>ATTN:  JAN BROCKMAN</rptOwnerStreet2>
            <rptOwnerCity>OMAHA</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68175</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000916302</rptOwnerCik>
            <rptOwnerName>UNITED OF OMAHA LIFE INSURANCE CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3300 MUTUAL OF OMAHA PLZ 3RD FLOOR LAW</rptOwnerStreet1>
            <rptOwnerStreet2>ATTN: JAN BROCKMAN</rptOwnerStreet2>
            <rptOwnerCity>OMAHA</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68175-1008</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Series I Mandatory Redeemable Preferred Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2021-05-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>384743</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>subsidiaries</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Mandatory Redeemable Preferred Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>94914</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4/A is being filed to correct the amount of securities owned by United of Omaha Life Insurance Company, 327,795 shares, and the amount of securities owned by Companion Life Insurance Company, 56,948 shares.  Mutual of Omaha Insurance Company is the direct parent of United of Omaha Life Insurance Company and the ultimate parent of Companion Life Insurance Company.</footnote>
        <footnote id="F2">This amount represents the number of shares acquired by United of Omaha Life Insurance Company on May 11, 2021.</footnote>
        <footnote id="F3">This Form 4/A is being filed to report the direct ownership of 94,914 shares owned by Mutual of Omaha Insurance Company.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Jan M. Brockman</signatureName>
        <signatureDate>2021-12-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
