Company: DAWN
Filing Date: 2025-01-10
Form Type: S-8
Source: 0001193125-25-004434
Chunk: 1

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-01-10
Form: S-8
Chunk 1
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REGISTRATION OF ADDITIONAL SHARES

PURSUANT TO GENERAL INSTRUCTION E

Day One
Biopharmaceuticals, Inc. (the “Registrant”) is filing this Registration Statement with the Securities and Exchange Commission (the “Commission”) to register (a) 5,131,836 additional shares of common
stock granted or available for issuance under the Registrant’s 2021 Equity Incentive Plan (the “2021 EIP”), pursuant to the provision of the 2021 EIP providing for an annual 5% automatic increase in the number of shares
reserved for issuance, and (b) 1,026,367 additional shares of common stock available for issuance under the Registrant’s 2021 Employee Stock Purchase Plan (the “2021 ESPP”), pursuant to the provision of the 2021 ESPP
providing for an annual 1% automatic increase in the number of shares reserved for issuance.

In accordance with General Instruction E of Form S-8, and only with respect to the common stock issuable under the 2021 EIP and 2021 ESPP, this Registration Statement hereby incorporates by reference the contents of the Registrant’s Registration Statements on
Form S-8 filed with the Commission on May 26, 2021 (Registration No. 333-256521), March 7, 2022 (Registration No. 333-263343), February
13, 2023 (Registration No. 269727) and January
4, 2024 (Registration No. 333-276372) to the extent not superseded hereby.

1

PART II INFORMATION REQUIRED IN THE REGISTRATION STATEMENT Item 3. Incorporation of Documents by Reference. The following documents filed by Day One Biopharmaceuticals, Inc. (the “ Registrant”) with the Commission pursuant to the Securities Act and the Securities Exchange Act of 1934, as amended (the “ Exchange Act”) are incorporated herein by reference:

| (b) | all other reports filed pursuant to Section 13(a) or 15(d) of the Exchange Act since the end of the fiscal 
 year covered by the Registrant’s Annual Report on Form 10-K referenced to in (a) above; and                |

| (c) | the description of the Registrant’s common stock contained in the Registrant’s registration statement                          
 on Form 8-A (File No. 001-40431) filed on May 24, 202