Company: DAWN
Filing Date: 2025-11-13
Form Type: SC TO-C
Source: 0001104659-25-110815
Chunk: 0

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-11-13
Form: SC TO-C
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported):(November 12, 2025 )

DAY ONE BIOPHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)</div>

| Delaware                     |     | 001-40431   |     | 83-2415215         |
| (State or other jurisdiction 
 of incorporation)            |     | -Commission 
 File Number |     | -IRS Employer      
 Identification No. |

| 1800 Sierra Point Parkway, Suite 200     |     |           |
| Brisbane, California                     |     |     94005 |
| (Address of principal executive offices) |     | -Zip Code |

<div align='center'>Registrant’s telephone number, including area code: (650) 484-0899

N/A

(Former name or former address, if changed since last report)</div>

Check the appropriate box below if the Form 8-K filing is intended
to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ¨ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |

| ¨ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) |

| x | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |

| ¨ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

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

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

Indicate by check mark whether the registrant is an emerging growth
company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12