X0508 4 2024-01-05 0 0001845337 Day One Biopharmaceuticals, Inc. DAWN 0001655962 York Charles N II 2000 SIERRA POINT PARKWAY, SUITE 501 BRISBANE CA 94005 0 1 0 0 COO, CFO and Secretary 0 Stock Option (right to buy Common Stock) 14.44 2024-01-05 4 A 0 162000 0.00 A 2034-01-04 Common Stock 162000 162000 D Restricted Stock Units 2024-01-05 4 A 0 106000 0.00 A Common Stock 106000 106000 D The option vests as to 1/48th of the total shares monthly, commencing February 5, 2024, 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. /s/ Charles N. York II 2024-01-09