X0306 4 2021-06-01 0 0001845337 Day One Biopharmaceuticals, Inc. DAWN 0001712417 Canaan XI L.P. 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT CT 06880 0 0 1 0 0001850694 Canaan Partners XI LLC 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT CT 06880 0 0 1 0 Common Stock 2021-06-01 4 C 0 7328497 A 10574366 D Common Stock 2021-06-01 4 C 0 148279 A 10722645 D Common Stock 2021-06-01 4 P 0 13000 16.00 A 10735645 D Series A Preferred Stock 2021-06-01 4 C 0 7328497 D Common Stock 7328497 0 D Series B Preferred Stock 2021-06-01 4 C 0 148279 D Common Stock 148279 0 D Each share of the Issuer's Series A Preferred Stock, which had no expiration date, automatically converted into one share of the Issuer's Common Stock at the close of the Issuer's initial public offering, for no additional consideration. These shares are held directly by Canaan XI L.P. (the "Canaan Fund"). The sole general partner of the Canaan Fund is Canaan Partners XI LLC ("Canaan XI", and together with the Canaan Fund, the "Canaan Entities"), and may be deemed to have sole voting, investment and dispositive power with respect to the shares held by the Canaan Fund. Investment and voting decisions with respect to the shares held by the Canaan Fund are made by the managers of Canaan XI, collectively. Canaan XI disclaims Section 16 beneficial ownership of the securities held by the Canaan Fund, except to the extent of its pecuniary interest therein, if any. Each share of the Issuer's Series B Preferred Stock, which had no expiration date, automatically converted into one share of the Issuer's Common Stock at the close of the Issuer's initial public offering, for no additional consideration. Exhibit 24 - Power of Attorney (incorporated by reference to the Power of Attorney filed as Exhibit 24 to the Form 3 filed by the Reporting Persons on May 26, 2021) Canaan XI L.P., By: Canaan Partners XI LLC, its general partner, By: /s/ Nancy Levenson, Attorney-in-Fact 2021-06-02 Canaan Partners XI LLC, By: /s/ Nancy Levenson, Attorney-in-Fact 2021-06-02