X0508 4 2026-01-30 0001845337 Day One Biopharmaceuticals, Inc. DAWN 0001863107 Bender Jeremy 1800 SIERRA POINT PARKWAY, SUITE 200 BRISBANE CA 94005 true true false false CHIEF EXECUTIVE OFFICER 0 Stock Option (right to buy Common Stock) 11.16 2026-01-30 4 A 0 355000 0 A 2036-01-29 Common Stock 355000 355000 D Restricted Stock Units 2026-01-30 4 A 0 237000 0 A Common Stock 237000 237000 D The option vests as to 1/48th of the total shares monthly, commencing February 28, 2026, subject to the Reporting Person's provision of service to the Issuer on each vesting date. Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement. The RSUs vest as to 1/16th of the total award in quarterly installments on February 15, May 15, August 15 and November 15, subject to the Reporting Person's provision of service to the Issuer on each vesting date. RSUs do not expire; they either vest or are canceled prior to the vesting date. /s/ Charles N. York II, as Attorney-in-Fact 2026-01-30