Cover Page - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Apr. 15, 2026 |
Jun. 30, 2025 |
|
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | true | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Document Period End Date | Dec. 31, 2025 | ||
| Document Fiscal Year Focus | 2025 | ||
| Document Fiscal Period Focus | FY | ||
| Entity Registrant Name | DAY ONE BIOPHARMACEUTICALS, INC. | ||
| Entity Central Index Key | 0001845337 | ||
| Entity File Number | 001-40431 | ||
| Entity Tax Identification Number | 83-2415215 | ||
| Entity Incorporation, State or Country Code | DE | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Well-known Seasoned Issuer | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity Shell Company | false | ||
| Entity Filer Category | Large Accelerated Filer | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | false | ||
| ICFR Auditor Attestation Flag | true | ||
| Entity Address, Address Line One | 1800 Sierra Point Parkway | ||
| Entity Address, Address Line Two | Suite 200 | ||
| Entity Address, City or Town | Brisbane | ||
| Entity Address, State or Province | CA | ||
| Entity Address, Postal Zip Code | 94005 | ||
| City Area Code | 650 | ||
| Local Phone Number | 484-0899 | ||
| Title of 12(b) Security | Common Stock, par value $0.0001 per share | ||
| Trading Symbol | DAWN | ||
| Security Exchange Name | NASDAQ | ||
| Entity Common Stock, Shares Outstanding | 103,334,169 | ||
| Document Financial Statement Error Correction [Flag] | false | ||
| Entity Public Float | $ 567.0 | ||
| Amendment Description | This Amendment No. 1 on Form 10-K/A (this “Amendment”) amends our Annual Report on Form 10-K for the year ended December 31, 2025, originally filed with the Securities and Exchange Commission (the “SEC”) on February 24, 2026 (the “Original Filing”). We are filing this Amendment pursuant to General Instruction G(3) of Form 10-K to include the information required by Part II and Part III of Form 10-K that we did not include in the Original Filing, as we do not intend to file a definitive proxy statement for an annual meeting of stockholders within 120 days of the end of our fiscal year ended December 31, 2025. In addition, in connection with the filing of this Amendment and pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), we are including with this Amendment new certifications of our principal executive officer and principal financial officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. Item 15 of Part IV has been amended to reflect the filing of these new certifications. Except as described above, no other changes have been made to the Original Filing. The Original Filing continues to speak as of the date of the Original Filing, and we have not updated the disclosures contained therein to reflect any events which occurred as of any date subsequent to the filing of the Original Filing.Unless otherwise noted or the context indicates otherwise, the terms “Day One,” the “Company,” “we,” “us,” and “our” refer to Day One Biopharmaceuticals, Inc., a Delaware corporation, together with its consolidated subsidiaries.As previously announced, on March 6, 2026, Servier Pharmaceuticals LLC, a Delaware limited liability company (“Parent”), Servier Detroit Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), Day One Biopharmaceuticals, Inc., a Delaware corporation (the “Company”), and Servier S.A.S., a French société par actions simplifiée, solely as a guarantor (“Guarantor”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), providing for the merger of Merger Sub with and into the Company (the “Merger”), with the Company surviving the Merger as a wholly owned subsidiary of Parent. |