Sec Form 4 Filing - BARRETT MICHAEL G. @ MAGNITE, INC. - 2021-08-26

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 BARRETT MICHAEL G. 2. Issuer Name and Ticker or Trading Symbol MAGNITE, INC. [ MGNI] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) CEO (Last) (First) (Middle) C/O MAGNITE, INC., 6080 CENTER DRIVE, 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 08/26/2021 (Street) LOS ANGELES, CA90045 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 08/26/2021 A 136,939 ( 1 ) A $ 0 1,479,368 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 ( 2 ) 08/26/2021 A 379,635 ( 3 ) ( 3 ) Common Stock 379,635 $ 0 ( 4 ) 379,635 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BARRETT MICHAEL G. C/O MAGNITE, INC. 6080 CENTER DRIVE, 4TH FLOOR LOS ANGELES, CA90045 X CEO Signatures /s/ Aaron Saltz, attorney-in-fact 08/30/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents restricted stock units that vest as to 1/3 on each of August 15, 2023, August 15, 2024 and August 15, 2025, 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 )Each performance stock unit ("PSU") represents a contingent right to receive on vesting one share of the Issuer's common stock. ( 3 )The PSUs are subject to both performance-based and time-based vesting requirements. The performance-based requirement for 1/3 of the units will be satisfied if the Issuer achieves share price targets of $60, $80 and $100 over 60 consecutive trading days during a performance period commencing on Aug. 26, 2022 and ending on Aug. 26, 2026, or on such earlier date as the Reporting Person is no longer serving as the Issuer's CEO or Executive Chairman of the Board of Directors. To the extent any of the performance-based requirements are met, the Reporting Person must also provide continued service to the Issuer through at least Aug. 26, 2024 to receive any shares of common stock underlying the PSUs and through Aug. 26, 2026 to receive all of the shares of common stock underlying the PSUs that have satisfied the applicable performance-based requirements. The grant may be subject to accelerated vesting in the event the Reporting Person's employment is terminated under certain circumstances. ( 4 )Equity grant under the Issuer's 2014 Equity Incentive Plan.

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).

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