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        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001720317</cik>
                    <ccc>XXXXXXXX</ccc>
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            <liveTestFlag>LIVE</liveTestFlag>



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        <issuerInfo>
            <issuerCik>0001701732</issuerCik>
            <issuerName>ALTAIR ENGINEERING INC.</issuerName>
            <secFileNumber>001-38263</secFileNumber>
            <issuerAddress>
                <ns2:street1>1820 East Big Beaver Road</ns2:street1>
                <ns2:city>Troy</ns2:city>
                <ns2:stateOrCountry>MI</ns2:stateOrCountry>
                <ns2:zipCode>48083</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>248-614-2400</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>TERESA A. HARRIS</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Director</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>8th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>620</noOfUnitsSold>
            <aggregateMarketValue>64542.00</aggregateMarketValue>
            <noOfUnitsOutstanding>85081191</noOfUnitsOutstanding>
            <approxSaleDate>11/05/2024</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <acquiredDate>11/05/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Stock Option Exercise</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>620</amountOfSecuritiesAcquired>
            <paymentDate>11/05/2024</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>TERESA A. HARRIS</name>
                <address>
                    <ns2:street1>1820 East Big Beaver Road</ns2:street1>
                    <ns2:city>Troy</ns2:city>
                    <ns2:stateOrCountry>MI</ns2:stateOrCountry>
                    <ns2:zipCode>48083</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>10/01/2024</saleDate>
            <amountOfSecuritiesSold>620</amountOfSecuritiesSold>
            <grossProceeds>58974.40</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>TERESA A. HARRIS</name>
                <address>
                    <ns2:street1>1820 East Big Beaver Road</ns2:street1>
                    <ns2:city>Troy</ns2:city>
                    <ns2:stateOrCountry>MI</ns2:stateOrCountry>
                    <ns2:zipCode>48083</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>09/03/2024</saleDate>
            <amountOfSecuritiesSold>620</amountOfSecuritiesSold>
            <grossProceeds>55614.00</grossProceeds>
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                <name>TERESA A. HARRIS</name>
                <address>
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                    <ns2:city>Troy</ns2:city>
                    <ns2:stateOrCountry>MI</ns2:stateOrCountry>
                    <ns2:zipCode>48083</ns2:zipCode>
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            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>08/06/2024</saleDate>
            <amountOfSecuritiesSold>620</amountOfSecuritiesSold>
            <grossProceeds>51193.40</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>11/05/2024</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>11/15/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Teresa Anita Harris</signature>
        </noticeSignature>
    </formData>
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144
0001720317
XXXXXXXX
LIVE
0001701732
ALTAIR ENGINEERING INC.
001-38263
1820 East Big Beaver Road
Troy
MI
48083
248-614-2400
TERESA A. HARRIS
Director
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
8th Floor
New York
NY
10004
620
64542.00
85081191
11/05/2024
NASDAQ
COMMON
11/05/2024
Stock Option Exercise
ISSUER
N
620
11/05/2024
Cash
N
TERESA A. HARRIS
1820 East Big Beaver Road
Troy
MI
48083
Common
10/01/2024
620
58974.40
TERESA A. HARRIS
1820 East Big Beaver Road
Troy
MI
48083
Common
09/03/2024
620
55614.00
TERESA A. HARRIS
1820 East Big Beaver Road
Troy
MI
48083
Common
08/06/2024
620
51193.40
11/05/2024
11/15/2023
/s/ Teresa Anita Harris