Sec Form 4 Filing - Messano Amy @ Altair Engineering Inc. - 2025-03-26

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Messano Amy 2. Issuer Name and Ticker or Trading Symbol Altair Engineering Inc. [ ALTR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Marketing Officer (Last) (First) (Middle) 1820 E. BIG BEAVER ROAD 3. Date of Earliest Transaction (MM/DD/YY) 03/26/2025 (Street) TROY, MI48083 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Class A Common Stock 03/26/2025 D( 1 ) 22,980 ( 2 ) D $ 113 ( 3 ) ( 4 ) 0 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Class A Common Stock Option $ 39.82 03/26/2025 D( 1 ) 5,635 ( 5 ) ( 6 )( 7 ) 06/02/2030 Class A Common Stock 5,635 ( 5 ) $ 73.18 0 D Class A Common Stock Option $ 52.03 03/26/2025 D( 1 ) 22,500 ( 8 ) ( 6 )( 9 ) 12/02/2030 Class A Common Stock 22,500 ( 8 ) $ 60.97 0 D Class A Common Stock Option $ 61.93 03/26/2025 D( 1 ) 4,856 ( 10 ) ( 6 )( 11 ) 03/15/2031 Class A Common Stock 4,856 ( 10 ) $ 51.07 0 D Class A Common Stock Option $ 61.79 03/26/2025 D( 1 ) 8,200 ( 12 ) ( 6 )( 13 ) 02/15/2032 Class A Common Stock 8,200 ( 12 ) $ 51.21 0 D Class A Common Stock Option $ 45.91 03/26/2025 D( 1 ) 24,000 ( 14 ) ( 6 )( 15 ) 12/15/2032 Class A Common Stock 24,000 ( 14 ) $ 67.09 0 D Class A Common Stock Option $ 65.19 03/26/2025 D( 1 ) 8,855 ( 16 ) ( 6 )( 17 ) 03/02/2033 Class A Common Stock 8,855 ( 16 ) $ 47.81 0 D Class A Common Stock Option $ 79.03 03/26/2025 D( 1 ) 9,208 ( 18 ) ( 6 )( 19 ) 03/15/2034 Class A Common Stock 9,208 ( 18 ) $ 33.97 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Messano Amy 1820 E. BIG BEAVER ROAD TROY, MI48083 Chief Marketing Officer Signatures /s/ Raoul Maitra, attorney-in-fact for Amy Messano 03/26/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On March 26, 2025, the Company was acquired by Siemens Industry Software Inc. ("Siemens") pursuant to the merger agreement entered into among the Company, Siemens, and Astra Merger Sub Inc., dated as of October 30, 2024. ( 2 )Includes 0 Class A Common Stock restricted stock units ("RSUs") that are unvested and scheduled to vest on or prior to December 31, 2025, and 10,826 RSUs that are unvested and scheduled to vest on or after January 1, 2026. ( 3 )Upon the consummation of the merger, each issued and outstanding share of the Company's Class A Common Stock ("Common Stock") was canceled and converted into the right receive $113.00 in cash without interest. Each RSU that was granted under the Company's 2017 Equity Incentive Plan (the "2017 Plan") that was outstanding immediately prior to the consummation of the merger and was scheduled to vest on or before December 31, 2025 was vested, canceled and converted into the right to receive $113.00 in cash without interest. ( 4 )(continued from footnote 3) Each RSU that was granted under the 2017 Plan that was outstanding immediately prior to the consummation of the merger, and scheduled to vest on or after January 1, 2026 was canceled and converted into the right to receive $113.00 in cash without interest, and will be paid on the last day of the calendar quarter preceding the quarter in which such RSU would have otherwise vested in accordance with the vesting schedule in effect immediately prior to the consummation of the merger, less any applicable withholding taxes, subject to acceleration in certain circumstances. ( 5 )This option is fully vested. ( 6 )Each option that was outstanding immediately prior to the consummation of the merger and was scheduled to vest on or before December 31, 2025 was vested, canceled and converted into the right to receive the cash value of the option. Each option that was outstanding immediately prior to the consummation of the merger, and scheduled to vest on or after January 1, 2026 was canceled and converted into a right to receive the cash value of the option, such cash value of the option to be paid on the last day of the calendar quarter preceding the quarter in which such option would have otherwise vested in accordance with the vesting schedule in effect immediately prior to the consummation of the merger, less any applicable withholding taxes, subject to acceleration in certain circumstances. ( 7 )This option represents an aggregate cash value of $412,369.30, representing the difference between the exercise price of the option and $113.00. ( 8 )This option is fully vested. ( 9 )This option represents an aggregate cash value of $1,371,825.00, representing the difference between the exercise price of the option and $113.00. ( 10 )This option is fully vested. ( 11 )This option represents an aggregate cash value of $247,995.92, representing the difference between the exercise price of the option and $113.00. ( 12 )Includes 0 shares of Common Stock underlying the options that are unvested and scheduled to vest on or prior to December 31, 2025, and 2,050 shares of Common Stock underlying the options that are unvested and scheduled to vest on or after January 1, 2026. ( 13 )This option represents an aggregate cash value of $419,922.00, representing the difference between the exercise price of the option and $113.00. ( 14 )Includes 12,000 shares of Common Stock underlying the options that are unvested and scheduled to vest on or prior to December 31, 2025, and 0 shares of Common Stock underlying the options that are unvested and scheduled to vest on or after January 1, 2026. ( 15 )This option represents an aggregate cash value of $1,610,160.00, representing the difference between the exercise price of the option and $113.00. ( 16 )Includes 0 shares of Common Stock underlying the options that are unvested and scheduled to vest on or prior to December 31, 2025, and 4,427 shares of Common Stock underlying the options that are unvested and scheduled to vest on or after January 1, 2026. ( 17 )This option represents an aggregate cash value of $423,357.55, representing the difference between the exercise price of the option and $113.00. ( 18 )Includes 0 shares of Common Stock underlying the options that are unvested and scheduled to vest on or prior to December 31, 2025, and 6,906 shares of Common Stock underlying the options that are unvested and scheduled to vest on or after January 1, 2026. ( 19 )This option represents an aggregate cash value of $312,795.76, representing the difference between the exercise price of the option and $113.00.

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