X0306 4 2021-06-16 0001701732 Altair Engineering Inc. ALTR 0001720686 Chouinard Brett R C/O ALTAIR ENGINEERING INC. 1820 E. BIG BEAVER RD. TROY MI 48083 1 1 See Remarks Class A Common Stock 2021-06-16 4 M 0 2006 3.64 A 17124 D Class A Common Stock 2021-06-16 4 M 0 1000 3.84 A 18124 D Class A Common Stock 2021-06-16 4 S 0 3006 64.063 D 15118 D Class A Common Stock 2021-06-16 4 S 0 1890 64.09 D 13228 D Stock Option (Right to Buy) 3.64 2021-06-16 4 M 0 2006 0 D 2026-05-17 Class A Common Stock 2006 0 D Stock Option (Right to Buy) 3.84 2021-06-16 4 M 0 1000 0 D 2025-12-17 Class A Common Stock 1000 0 D Includes 9,972 Class A Common Stock restricted stock units that are unvested. The sale of the shares of Class A Common Stock were made pursuant to a plan intended to comply with Rule 10b5-1 of the Exchange Act, previously entered into on May 13, 2021. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.77 to $64.64 per share, inclusive. The reporting person undertakes to provide to Altair Engineering Inc., any security holder of Altair Engineering Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth herein. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.77 to $64.64 per share, inclusive. The reporting person undertakes to provide to Altair Engineering Inc., any security holder of Altair Engineering Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth herein. The options vested in 4 equal annual installments commencing May 17, 2017. The options vested in 4 equal annual installments commencing December 17, 2016. Chief Technical Officer, Modeling/Visualization /s/ Raoul Maitra, attorney-in-fact for Brett R. Chouinard 2021-06-17