SCHEDULE 13G 0001974915 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 12/31/2025 0001845337 Day One Biopharmaceuticals, Inc. 23954D109 1800 SIERRA POINT PARKWAY, SUITE 200 BRISBANE CA 94005 Rule 13d-1(b) Vestal Point Capital, LP DE 0.00 5200000.00 0.00 5200000.00 5200000.00 N 5.1 IA PN Ryan Wilder X1 0.00 5200000.00 0.00 5200000.00 5200000.00 N 5.1 HC IN Day One Biopharmaceuticals, Inc. 1800 Sierra Point Parkway, Suite 200, Brisbane, California 94005. This statement is filed by: (i) Vestal Point Capital, LP (the "Investment Manager"), a Delaware limited partnership, and the investment adviser to a certain fund and a managed account (the "Vestal Point Fund and Account"), with respect to the shares of common stock, par value $0.0001 per share (the "Common Stock"), of Day One Biopharmaceuticals, Inc.. (the "Company") directly held by the Vestal Point Fund and Account; and (ii) Mr. Ryan Wilder ("Mr. Wilder"), the Chief Investment Officer and Managing Partner of the Investment Manager and the Managing Member of Vestal Point Capital, LLC, the general partner of the Investment Manager, with respect to the shares of Common Stock directly held by the Vestal Point Fund and Account. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." The filing of this statement should not be construed as an admission that any of the foregoing persons or any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, the beneficial owner of the securities reported herein. The address of the business office of each of the Reporting Persons is 632 Broadway, Suite 602, New York, NY 10012. The Investment Manager is a Delaware limited partnership. Mr. Wilder is a citizen of the United States. N IA HC The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentage set forth in this Schedule 13G is calculated based upon an aggregate of 102,675,502 shares of Common Stock outstanding as of October 31, 2025, as reported in the Company's Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2025, filed with the Securities and Exchange Commission on November 4, 2025. 5.1% The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference. Y N See Item 2(a). The Vestal Point Fund and Account have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the shares of Common Stock reported herein. Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Exhibit 99.1: Joint Filing Agreement Vestal Point Capital, LP /s/ Ryan Wilder 02/17/2026 Ryan Wilder /s/ Ryan Wilder 02/17/2026