Company: DAWN
Filing Date: 2025-03-06
Form Type: 10-K/A
Source: 0000950170-25-034878
Chunk: 0

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-03-06
Form: 10-K/A
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM10-K/A

(Amendment No. 1)</div>

(Mark One)

| ☒ | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |

<div align='center'>For the fiscal year endedDecember 31, 2024

OR</div>

| ☐ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM                      TO |

<div align='center'>Commission File Number001-40431

DAY ONE BIOPHARMACEUTICALS, INC.

(Exact name of Registrant as specified in its Charter)</div>

| Delaware                                                      |                         83-2415215 |
| (State or other jurisdiction ofincorporation or organization) | -I.R.S. EmployerIdentification No. |
| 1800 Sierra Point Parkway, Suite 200Brisbane, CA              |                              94005 |
| (Address of principal executive offices)                      |                          -Zip Code |

<div align='center'>Registrant’s telephone number, including area code:

(650)484-0899</div>

Securities registered pursuant to Section 12(b) of the Act:

| Title of each class                       |     | TradingSymbol(s) |     | Name of each exchange on which registered |
| Common Stock, par value $0.0001 per share |     | DAWN             |     | Nasdaq Global Select Market               |

Securities registered pursuant to Section 12(g) of the Act:None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.Yes☒No☐

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐No☒

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past