Sec Form 3 Filing - Evans Katie Seitz @ MAGNITE, INC. - 2020-09-21

FORM 3 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 Evans Katie Seitz 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 Operating Officer (Last) (First) (Middle) C/O MAGNITE, INC., 12181 BLUFF CREEK DRIVE, 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/21/2020 (Street) LOS ANGELES, CA90094 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 520,271 D ( 1 )

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 Stock Option (Right to Buy) $ 3.96 ( 2 ) 02/03/2021 Common Stock 1,442 D Stock Option (Right to Buy) $ 3.96 ( 2 ) 06/08/2021 Common Stock 1,442 D Stock Option (Right to Buy) $ 4.64 ( 2 ) 07/26/2022 Common Stock 2,884 D Stock Option (Right to Buy) $ 4.64 ( 2 ) 07/19/2022 Common Stock 2,884 D Stock Option (Right to Buy) $ 5.46 ( 2 ) 03/05/2023 Common Stock 7,212 D Stock Option (Right to Buy) $ 7.74 ( 2 ) 07/31/2023 Common Stock 5,410 D Stock Option (Right to Buy) $ 3.95 ( 2 ) 12/05/2023 Common Stock 22,971 D Stock Option (Right to Buy) $ 3.61 ( 3 ) 02/27/2028 Common Stock 56,137 D Stock Option (Right to Buy) $ 5.16 ( 4 ) 02/28/2029 Common Stock 33,546 D Stock Option (Right to Buy) $ 5.28 ( 5 ) 04/01/2030 Common Stock 69,470 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Evans Katie Seitz C/O MAGNITE, INC. 12181 BLUFF CREEK DRIVE, 4TH FLOOR LOS ANGELES, CA90094 Chief Operating Officer Signatures /s/ Aaron Saltz, Attorney-in-Fact 09/25/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes (i) 33,812 shares underlying Restricted Stock Units ("RSUs") which will vest on February 14, 2021; (ii) 13,871 shares underlying RSUs which will vest in two equal installments on each of February 14, 2021 and February 14, 2022; (iii) 37,569 shares underlying RSUs which will vest in three equal installments on each of February 14, 2021, February 14, 2022 and February 14, 2023; (iv) 92,396 shares that will vest as follows: 25,024 shares on May 15, 2021, 5,775 shares on each August 15, November 15 and February 15 thereafter until February 15, 2024, and 3,847 shares on May 15, 2024; and (v) 102,662 shares that vest in two equal installments on each of April 1, 2021 and April 1, 2022. ( 2 )Immediately exercisable. ( 3 )25% of the total number of shares underlying this option vested on February 14, 2019 and the remaining shares vest 1/36 per month over the next 36 months thereafter, subject to continued service to the Issuer through each vesting date. ( 4 )25% of the total number of shares underlying this option vested on February 14, 2020 and the remaining shares vest 1/36 per month over the next 36 months thereafter, subject to continued service to the Issuer through each vesting date. ( 5 )25% of the total number of shares underlying this option will vest on April 1, 2021 and the remaining shares vest 1/36 per month over the next 36 months thereafter, subject to continued service to the Issuer through each vesting date.

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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