The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

 Names of Reporting Persons

 George J. Christ

 Check the Appropriate Box if a Member of a Group

 (a) ☐  (b) ☐

 SEC Use Only

 Citizenship or Place of Organization

 United States

Number of

Shares  Beneficially 

Owned By

Each

Reporting

Person

With

 Sole Voting Power:

 9,450,684*

 Shared Voting Power:

 0

 Sole Dispositive Power:

 9,450,684*

 Shared Dispositive Power:

 0

 Aggregate Amount Beneficially Owned by Each Reporting Person

 9,450,684*

 Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions):

 ☐

 Percent of Class Represented by Amount in Row (9)

 13.9% *

 Type of Reporting Person

 IN

Based on the information provided by Altair Engineering Inc. (the “Company”) to the Reporting Persons (as defined below), on September 30, 2024 (the “Event Date”), there were 59,517,279 shares of the Company’s Class A common stock, $0.0001 par value per share (the “Class A Common Stock”) outstanding. George J. Christ (“Mr. Christ”) is the Trustee of the Christ Revocable Trust dated May 8, 2015 (the “Christ Trust”), and the Manager of GC Investments, LLC (the “GC LLC” and, collectively with Mr. Christ and the Christ Trust, the “Reporting Persons”). Mr. Christ is also the Co-Trustee of The Dana Christ Irrevocable Trust Dated May 8, 2015 (the “Dana Trust”) and the Co-Trustee of The Lauren Christ Irrevocable Trust Dated May 8, 2015 (the “Lauren Trust”). As of the Event Date, the Reporting Persons may be deemed to beneficially own an aggregate of 9,450,684 shares of Class A Common Stock. The number of shares of Class A Common Stock reported above consists of (i) 4,481,778 shares of Class A Common Stock issuable upon conversion of 4,481,778 shares of the Company’s Class B common stock, $0.0001 par value per share (the “Class B Common Stock”), of the Company held by the Christ Trust, (ii) 4,044,004 shares of Class A Common Stock issuable upon conversion of 4,044,004 shares of Class B Common Stock held by the GC LLC, (iii) 400,000 shares of Class A Common Stock held by the GC LLC, (iv) 149,954 shares of Class A Common Stock held by the Christ Trust, (v) 187,475 shares of Class A Common Stock held by the Dana Trust and (vi) 187,475 shares of Class A Common Stock held by the Lauren Trust. The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to voting and conversion rights. Each share of Class A Common Stock is entitled to one vote per share and each share of Class B Common Stock is entitled to ten votes per share. Each share of Class B Common Stock is immediately convertible, at the option of the Reporting Persons, into one share of Class A Common Stock and shall automatically convert into Class A Common Stock upon the occurrence of certain events. Please see the Company’s Registration Statement filed with the Securities and Exchange Commission on Form S-1 (File No. 333-220710) for a description of the conversion rights. Thus, as of the Event Date, for purposes of Rule 13d-3 under the Securities Exchange Act of 1934, as amended, the Reporting Persons may be deemed to beneficially own 13.9% of the shares of Class A Common Stock issued and outstanding. The percentage was obtained by dividing (a) the number of shares of Class A Common Stock beneficially owned by the Reporting Persons as set forth in Row 9 by (b) the sum of (i) 59,517,279 shares of Class A Common Stock outstanding as of the Event Date and (ii) the 8,525,782 shares of Class A Common Stock issuable upon conversion of the Class B Common Stock.

 Names of Reporting Persons

 Christ Revocable Trust dated May 8, 2015

 Check the Appropriate Box if a Member of a Group

 (a) ☐  (b) ☐

 SEC Use Only

 Citizenship or Place of Organization

 United States

Number of

Shares  Beneficially 

Owned By

Each

Reporting

Person

With

 Sole Voting Power:

 4,481,778*

 Shared Voting Power:

 0

 Sole Dispositive Power:

 4,481,778*

 Shared Dispositive Power:

 0

 Aggregate Amount Beneficially Owned by Each Reporting Person

 4,481,778*

 Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions):

 ☐

 Percent of Class Represented by Amount in Row (9)

 7.0% *

 Type of Reporting Person

 OO

Based on the information provided by Altair Engineering Inc. (the “Company”) to the Reporting Person (as defined below), on September 30, 2024 (the “Event Date”), there were 59,517,279 shares of the Company’s Class A common stock, $0.0001 par value per share (the “Class A Common Stock”) outstanding. George J. Christ (“Mr. Christ”) is the Trustee of the Christ Revocable Trust dated May 8, 2015 (the “Christ Trust”). As of the Event Date, the Christ Trust may be deemed to beneficially own an aggregate of 4,481,778 shares of Class A Common Stock. The number of shares of Class A Common Stock reported above consists of 4,481,778 shares of Class A Common Stock issuable upon conversion of 4,481,778 shares of the Company’s Class B common stock, $0.0001 par value per share (the “Class B Common Stock”). The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to voting and conversion rights. Each share of Class A Common Stock is entitled to one vote per share and each share of Class B Common Stock is entitled to ten votes per share. Each share of Class B Common Stock is immediately convertible, at the option of the Reporting Person, into one share of Class A Common Stock and shall automatically convert into Class A Common Stock upon the occurrence of certain events. Please see the Company’s Registration Statement filed with the Securities and Exchange Commission on Form S-1 (File No. 333-220710) for a description of the conversion rights. Thus, as of the Event Date, for purposes of Rule 13d-3 under the Securities Exchange Act of 1934, as amended, the Christ Trust may be deemed to beneficially own 7.0% of the shares of Class A Common Stock issued and outstanding. The percentage was obtained by dividing (a) the number of shares of Class A Common Stock beneficially owned by the Christ Trust as set forth in Row 9 by (b) the sum of (i) 59,517,279 shares of Class A Common Stock outstanding as of the Event Date and (ii) the 4,481,778 shares of Class A Common Stock issuable upon conversion of the Class B Common Stock beneficially owned by the Christ Trust.

 Names of Reporting Persons

 GC Investments, LLC

 Check the Appropriate Box if a Member of a Group

 (a) ☐  (b) ☐

 SEC Use Only

 Citizenship or Place of Organization

 United States

Number of

Shares  Beneficially 

Owned By

Each

Reporting

Person

With

 Sole Voting Power:

 4,044,004*

 Shared Voting Power:

 0

 Sole Dispositive Power:

 4,044,004*

 Shared Dispositive Power:

 0

 Aggregate Amount Beneficially Owned by Each Reporting Person

 4,044,004*

 Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions):

 ☐

 Percent of Class Represented by Amount in Row (9)

 6.4%

 Type of Reporting Person

 OO

Based on the information provided by Altair Engineering Inc. (the “Company”) to the Reporting Person (as defined below), on September 30, 2024 (the “Event Date”), there were 59,517,279 shares of the Company’s Class A common stock, $0.0001 par value per share (the “Class A Common Stock”), outstanding. George J. Christ (“Mr. Christ”) is the Manager of GC Investments, LLC (the “GC LLC”). As of the Event Date, the GC LLC may be deemed to beneficially own an aggregate of 4,044,004 shares of Class A Common Stock. The number of shares of Class A Common Stock reported above consists of 4,044,004 shares of Class A Common Stock issuable upon conversion of 4,044,004 shares of the Company’s Class B common stock, $0.0001 par value per share (the “Class B Common Stock”). The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to voting and conversion rights. Each share of Class A Common Stock is entitled to one vote per share and each share of Class B Common Stock is entitled to ten votes per share. Each share of Class B Common Stock is immediately convertible, at the option of the Reporting Person, into one share of Class A Common Stock and shall automatically convert into Class A Common Stock upon the occurrence of certain events. Please see the Company’s Registration Statement filed with the Securities and Exchange Commission on Form S-1 (File No. 333-220710) for a description of the conversion rights. Thus, as of the Event Date, for purposes of Rule 13d-3 under the Securities Exchange Act of 1934, as amended, the GC LLC may be deemed to beneficially own 6.4% of the shares of Class A Common Stock issued and outstanding. The percentages were obtained by dividing (a) the number of shares of Class A Common Stock beneficially owned by the GC LLC as set forth in Row 9 by (b) the sum of (i) 59,517,279 shares of Class A Common Stock outstanding as of the Event Date and (ii) the 4,044,004 shares of Class A Common Stock issuable upon conversion of the Class B Common Stock beneficially owned by the GC LLC.

Name Of Issuer:

Address of Issuer’s Principal Executive Offices:

Name of Person Filing:

Address of Principal Business Office or, if None, Residence:

Citizenship:

Title of Class of Securities:

CUSIP No.:

If This Statement Is Filed Pursuant to Section 240.13d-1(b) or 240.13d-2(b) or (c), check whether the Person Filing is a:

Ownership:

(a)   Amount Beneficially Owned:

(b)   Percent of Class:

(c)   Number of Shares as to which the person has:

(i) Sole power to vote or to direct the vote:

(ii)  Shared power to vote or to direct the vote

(iii)  Sole power to dispose or to direct the disposition of:

(iv) Shared power to dispose or to direct the disposition of

(a)   Amount Beneficially Owned:

(b)   Percent of Class:

(c)   Number of Shares as to which the person has:

(i) Sole power to vote or to direct the vote:

(ii)  Shared power to vote or to direct the vote

(iii)  Sole power to dispose or to direct the disposition of:

(iv) Shared power to dispose or to direct the disposition of

(a)   Amount Beneficially Owned:

(b)   Percent of Class:

(c)   Number of Shares as to which the person has:

(i) Sole power to vote or to direct the vote:

(ii)  Shared power to vote or to direct the vote

(iii)  Sole power to dispose or to direct the disposition of:

(iv) Shared power to dispose or to direct the disposition of

This report on Schedule 13G, is being jointly filed by (i) the Christ Trust, (ii) the GC LLC, and (iii) Mr. Christ, as the Trustee of the Christ Trust, the Manager of the GC LLC, the Co-Trustee of the Dana Trust and the Co-Trustee of the Lauren Trust.

Ownership of Five Percent or Less of a Class

Ownership of More Than Five Percent on Behalf of Another Person

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person

Identification and Classification of Members of the Group

Notice of Dissolution of Group

Certification

A power of attorney was previously filed with the Commission and is incorporated herein by reference to Exhibits 99.2, 99.3 and 99.4 to the Schedule 13G filed by George J. Christ on February 14, 2018.

Exhibit