X0306 4 2023-02-15 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 Common Stock 2023-02-15 4 M 0 1375 A 270185 D Common Stock 2023-02-15 4 M 0 2250 A 272435 D Common Stock 2023-02-16 4 S 0 930 19.573 D 271505 D Restricted Stock Units 2023-02-15 4 M 0 1375 0.00 D Common Stock 1375 15125 D Restricted Stock Units 2023-02-15 4 M 0 2250 0.00 D Common Stock 2250 33750 D Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration. The sale of shares is for the sole purpose of covering the Reporting Person's tax liability with respect to the settlement of RSUs. The RSUs will 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 2023-02-17