# EDGAR Filing Document

**Accession Number:** 0001845337
**File Stem:** 0001193125-26-202385
**Filing Date:** 2026-5
**Character Count:** 2973
**Document Hash:** 1dc8ef4dd7c0d0aa240dd120e8e99f33
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-202385.hdr.sgml**: 20260504

**ACCESSION NUMBER**: 0001193125-26-202385

**CONFORMED SUBMISSION TYPE**: 15-12G

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260504

**DATE AS OF CHANGE**: 20260504

**EFFECTIVENESS DATE**: 20260504

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Day One Biopharmaceuticals, Inc.
- **CENTRAL INDEX KEY:** 0001845337
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 832415215
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 15-12G
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-40431
- **FILM NUMBER:** 26934482

**BUSINESS ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005
- **BUSINESS PHONE:** 650 484-0899

**MAIL ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Day One Biopharmaceuticals Holding Co LLC
- **DATE OF NAME CHANGE:** 20210209

**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**Washington, D.C. 20549** 

**FORM 15** 

**CERTIFICATION AND NOTICE OF TERMINATION OF REGISTRATION** 

**UNDER SECTION 12(g) OF THE SECURITIES EXCHANGE ACT OF 1934** 

**OR SUSPENSION OF DUTY TO FILE REPORTS UNDER SECTIONS 13 AND 15(d)** 

**OF THE SECURITIES EXCHANGE ACT OF 1934.** 

**Commission File Number 001-40431**

## DAY ONE BIOPHARMACEUTICALS, INC.
**(Exact name of registrant as specified in its charter)** 

**1800 Sierra Point Parkway, Suite 200** 

**Brisbane, CA 94005** 

**Telephone: (650) 484-0899**

**(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)** 

**Common stock, $0.0001 par value per share** 

**(Title of each class of securities covered by this Form)** 

**None** 

**(Titles of all other classes of securities for which a duty to file reports under section 13(a) or 15(d) remains)** 

Please place an X in the box(es) to designate the appropriate rule provision(s) relied upon to terminate or suspend the duty to file reports:

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| | |
|:---|:---|
|  Rule 12g-4(a)(1) | ☒ |
|  Rule 12g-4(a)(2) | ☐ |
|  Rule 12h-3(b)(1)(i) | ☒ |
|  Rule 12h-3(b)(1)(ii) | ☐ |
|  Rule 15d-6 | ☐ |
|  Rule 15d-22(b) | ☐ |

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Approximate number of holders of record as of the certification or notice date: <u>One holder</u>

Pursuant to the requirements of the Securities Exchange Act of 1934, Day One Biopharmaceuticals, Inc. has caused this certification/notice to be signed on its behalf by the undersigned duly authorized person.

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| | | |
|:---|:---|:---|
| Date: May 4, 2026 | **Day One Biopharmaceuticals, Inc.** | **Day One Biopharmaceuticals, Inc.** |
|  | By: | /s/ David Lee |
|  | Name: | David Lee |
|  | Title: | President and Secretary |

---