SCHEDULE 13G/A 0000902664-20-001129 0001410830 XXXXXXXX LIVE 6 Class A Common Stock, $0.0001 par value per share 03/31/2025 0001701732 Altair Engineering Inc. 021369103 1820 E. BIG BEAVER ROAD TROY MI 48083 Rule 13d-1(b) Matrix Capital Management Company, LP DE 0.00 0.00 0.00 0.00 0.00 N 0 IA PN David E. Goel X1 0.00 0.00 0.00 0.00 0.00 N 0 HC IN Altair Engineering Inc. 1820 East Big Beaver Road, Troy, Michigan 48083 This statement is filed by: (i) Matrix Capital Management Company LP (the "Investment Manager"), a Delaware limited partnership, and the investment adviser to Matrix Capital Management Master Fund, LP (the "Matrix Fund"), with respect to the shares of class A common stock, $0.0001 par value per share (the "Shares") of Altair Engineering Inc. (the "Company") that were directly held by the Matrix Fund; and (ii) Mr. David E. Goel (the "Mr. Goel"), the Managing General Partner of the Investment Manager, with respect to the Shares that were directly held by the Matrix Fund. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons". The address of the business office of each of the Reporting Persons is Bay Colony Corporate Center, 1000 Winter Street, Suite 4500, Waltham, MA 02451. The Investment Manager is a Delaware limited partnership. Mr. Goel is a citizen of the United States. N IA HC The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. 0% The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference. N Y Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Matrix Capital Management Company, LP /s/ David E. Goel 04/07/2025 David E. Goel /s/ David E. Goel 04/07/2025