X0306 4 2021-08-16 0 0001595974 MAGNITE, INC. MGNI 0001523288 Day David C/O MAGNITE, INC. 6080 CENTER DRIVE, 4TH FLOOR LOS ANGELES CA 90045 0 1 0 0 Chief Financial Officer Common Stock 2021-08-16 4 S 0 5177 26.82 D 268349 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