X0306 4 2021-08-16 0 0001595974 MAGNITE, INC. MGNI 0001700262 Evans Katie Seitz C/O MAGNITE, INC. 6080 CENTER DRIVE, 4TH FLOOR LOS ANGELES CA 90045 0 1 0 0 Chief Operating Officer Common Stock 2021-08-16 4 S 0 3329 26.82 D 418934 D Represents the non-discretionary sale 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 2021-08-18