X0306 4 2021-02-01 0 0001845337 Day One Biopharmaceuticals, Inc. DAWN 0001673237 Grant Papanek Julie 395 OYSTER POINT BLVD, SUITE 217 SOUTH SAN FRANCISCO CA 94080 1 0 0 0 Common Stock 2021-06-01 4 C 0 7328497 A 10574366 I By Canaan XI, L.P. Common Stock 2021-06-01 4 C 0 148279 A 10722645 I By Canaan XI, L.P. Common Stock 2021-06-01 4 P 0 13000 16.00 A 10735645 I By Canaan XI, L.P. Common Stock 465000 D Series B Preferred Stock 2021-02-01 4 A 0 148279 A Common Stock 148279 148279 I By Canaan XI, L.P. Stock Option (right to buy Common Stock) 16.00 2021-05-26 4 A 0 63000 0.00 A 2031-05-25 Common Stock 63000 63000 D Series A Preferred Stock 2021-06-01 4 C 0 7328497 0.00 D Common Stock 7328497 0 I By Canaan XI, L.P. Series B Preferred Stock 2021-06-01 4 C 0 148279 0.00 D Common Stock 148279 0 I By Canaan XI, L.P. The shares of the Issuer's Series A Preferred Stock automatically converted on a one-for-one basis into shares of the Issuer's Common Stock on May 26, 2021 in connection with the closing of the Issuer's sale of its Common Stock in its firm commitment initial public offering (the "IPO") pursuant to a registration statement on Form S-1 (File No. 333-255754) under the Securities Act of 1933, as amended (the "Registration Statement"), and had no expiration date. Represents securities held by Canaan XI, L.P. ("Canaan LP"). The Reporting Person, as a non-managing member of Canaan LP's general partner, Canaan Partners XI LLC, disclaims beneficial ownership of such securities except to the extent of her pecuniary interest therein, if any. The shares of the Issuer's Series B Preferred Stock automatically converted on a one-for-one basis into shares of the Issuer's Common Stock on May 26, 2021 in connection with the closing of the Issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. The Reporting Person is reporting the purchase of these securities pursuant to Rule 16a-2(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Each share of Series B Preferred Stock automatically converted into one share of Common Stock at the close of the Issuer's IPO and has no expiration date. The number of securities reported reflects the 1 to 2.325 stock split of the Issuer's Common Stock and convertible preferred stock that was effected on May 23, 2021. The Reporting Person is reporting the acquisition of these securities pursuant to Rule 16a-2(a) of the Exchange Act. The option vests as to 1/36th of the total shares on each monthly anniversary, beginning on June 23, 2021, subject to the Reporting Person's provision of service to the Issuer on each vesting date. /s/ Julie Papanek Grant 2021-06-03