X0306 4 2022-05-15 0 0001595974 MAGNITE, INC. MGNI 0001865116 Buckley Sean Patrick C/O MAGNITE, INC. 1250 BROADWAY, 15TH FLOOR NEWYORK NY 10001 0 1 0 0 Chief Revenue Officer Common Stock 2022-05-15 4 F 0 6525 10.59 D 223779 D 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 2022-05-17