Sec Form 4 Filing - Buonasera David @ MAGNITE, INC. - 2023-02-28

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 Buonasera David 2. Issuer Name and Ticker or Trading Symbol MAGNITE, INC. [ MGNI] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Technology Officer (Last) (First) (Middle) C/O MAGNITE, INC., 1250 BROADWAY, 15TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 02/28/2023 (Street) NEW YORK, NY10001 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 Common Stock 02/28/2023 A 46,873 ( 1 ) A $ 0 ( 2 ) 221,557 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 Performance Stock Units ( 3 ) 02/28/2023 A 18,152 ( 4 ) ( 4 ) Common Stock 18,152 $ 0 ( 2 ) 18,152 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Buonasera David C/O MAGNITE, INC. 1250 BROADWAY, 15TH FLOOR NEW YORK, NY10001 Chief Technology Officer Signatures /s/ Aaron Saltz, attorney-in-fact 03/02/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents restricted stock units that vest as follows: 13,671 on May 15, 2024, 2,930 on each August 15, November 15, February 15 and May 15 thereafter until February 15, 2027 and 972 on May 15, 2027, subject to continued service to the Issuer through each vesting date. This equity grant may be subject to accelerated vesting in the event the Reporting Person's employment is terminated under certain circumstances. ( 2 )Equity grant under the Company's 2014 Equity Incentive Plan. ( 3 )Each performance stock unit ("PSU") represents a contingent right to receive on vesting one share of the Issuer's common stock. ( 4 )Vesting of the PSU will be determined based on the Issuer's total stockholder return ("TSR") for the three-year period commencing January 1, 2023 relative to the TSRs of the companies in the Russell 2000 index, over that period. The number of PSUs reported in column 5 reflects the target number of PSUs subject to the award. The award is eligible to vest as to 0% to 150% of the target number of PSUs.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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