X0508 4 2023-11-15 0 0001595974 MAGNITE, INC. MGNI 0001100612 BARRETT MICHAEL G. C/O MAGNITE, INC. 1250 BROADWAY, 15TH FLOOR NEW YORK NY 10001 1 1 0 0 CEO 1 Common Stock 2023-11-15 4 S 0 75000 7.80 D 1219203 D Common Stock 2023-11-15 4 F 0 11362 7.89 D 1207841 D These sales were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 2, 2023. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $7.565 to $7.955, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range set forth in this footnote. Represents the non-discretionary forfeiture of shares on behalf of the Reporting Person pursuant to an arrangement mandated by the Issuer to cover the tax withholding obligations associated with the vesting of restricted stock units. /s/ Aaron Saltz, attorney-in-fact 2023-11-17