# EDGAR Filing Document

**Accession Number:** 0001845337
**File Stem:** 0001193125-26-153054
**Filing Date:** 2026-4
**Character Count:** 17235
**Document Hash:** 148f1914e4116cb2d36614923b52b525
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-153054.hdr.sgml**: 20260413

**ACCESSION NUMBER**: 0001193125-26-153054

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260413

**DATE AS OF CHANGE**: 20260413

**SUBJECT COMPANY**: 

**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:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-92582
- **FILM NUMBER:** 26858448

**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
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** AI Day1 LLC
- **CENTRAL INDEX KEY:** 0001863302

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 40 WEST 57TH STREET
- **STREET 2:** 28TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10019
- **BUSINESS PHONE:** 212-247-6400

**MAIL ADDRESS:**
- **STREET 1:** 40 WEST 57TH STREET
- **STREET 2:** 28TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10019

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** AI Day 1 LLC
- **DATE OF NAME CHANGE:** 20210520

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## SCHEDULE 13D

### Under the Securities Exchange Act of 1934

**(Amendment No. 5)**

**Day One Biopharmaceuticals, Inc.**

*(Name of Issuer)*

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

*(Title of Class of Securities)*

**—**

*(CUSIP Number)*

**Alejandro Moreno**<br>c/o Access Industries, Inc.<br>40 West 57th Street, 28th Floor<br>New York NY 10019<br>(212) 247-6400

*(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)*

**04/09/2026**

*(Date of Event Which Requires Filing of this Statement)*

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**AI Day1 LLC** | Name of reporting person<br>**AI Day1 LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**12929322.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**12929322.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**12.52%** | Percent of class represented by amount in Row (11)<br>**12.52%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for Reporting Person:** (1) All percentages of ownership of Common Stock by the Reporting Persons presented in this Statement are based on 103,297,691 shares of Common Stock outstanding as of February 19, 2026, as reported in the Issuer's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the Securities and Exchange Commission (the "SEC") on February 24, 2026.

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Access Industries Holdings LLC** | Name of reporting person<br>**Access Industries Holdings LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**12929322.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**12929322.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**12.52%** | Percent of class represented by amount in Row (11)<br>**12.52%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for Reporting Person:** (1) All percentages of ownership of Common Stock by the Reporting Persons presented in this Statement are based on 103,297,691 shares of Common Stock outstanding as of February 19, 2026, as reported in the Issuer's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC on February 24, 2026.

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Access Industries Management, LLC** | Name of reporting person<br>**Access Industries Management, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**12929322.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**12929322.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**12.52%** | Percent of class represented by amount in Row (11)<br>**12.52%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for Reporting Person:** (1) All percentages of ownership of Common Stock by the Reporting Persons presented in this Statement are based on 103,297,691 shares of Common Stock outstanding as of February 19, 2026, as reported in the Issuer's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC on February 24, 2026.

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Len Blavatnik** | Name of reporting person<br>**Len Blavatnik** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**12929322.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**12929322.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | Aggregate amount beneficially owned by each reporting person<br>**12929322.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**12.52%** | Percent of class represented by amount in Row (11)<br>**12.52%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for Reporting Person:** (1) All percentages of ownership of Common Stock by the Reporting Persons presented in this Statement are based on 103,297,691 shares of Common Stock outstanding as of February 19, 2026, as reported in the Issuer's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC on February 24, 2026.

**Item 1. Security and Issuer**

**(a) Title of Class of Securities:**
Common Stock, par value $0.0001 per share

**(b) Name of Issuer:**
Day One Biopharmaceuticals, Inc.

**(c) Address of Issuer's Principal Executive Offices:**
1800 Sierra Point Parkway, Suite 200, Brisbane, CA, 94005

This Amendment No. 5 to Schedule 13D is being filed by AI Day1 LLC ("AI Day1"), Access Industries Holdings LLC ("AIH"), Access Industries Management, LLC ("AIM") and Len Blavatnik (collectively, the "Reporting Persons", and each, a "Reporting Person"), in respect of the common stock, par value $0.0001 per share (the "Common Stock"), of Day One Biopharmaceuticals, Inc. (the "Issuer").

The Schedule 13D filed with the Securities and Exchange Commission ("SEC") on June 9, 2021, as amended and supplemented by Amendment No. 1 to the Schedule 13D filed by the Reporting Persons with the SEC on June 21, 2022, Amendment No. 2 to the Schedule 13D filed by the Reporting Persons with the SEC on June 12, 2023, Amendment No. 3 to the Schedule 13D filed by the Reporting Persons with the SEC on October 20, 2023 and Amendment No. 4 to the Schedule 13D filed by the Reporting Persons with the SEC on August 1, 2024 (together, the "Schedule") is hereby amended and supplemented by the Reporting Persons as set forth below in this Amendment No. 5. This amendment is filed by the Reporting Persons in accordance with Rule 13d-2 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and refers only to information that has materially changed since the filing of the Schedule. The items identified below, or the particular paragraphs of such items which are identified below, are amended as set forth below. Unless otherwise indicated, all capitalized terms used and not defined herein have the respective meanings assigned to them in the Schedule.

**Item 4. Purpose of Transaction**

The disclosure in Item 4 is hereby supplemented by adding the following at the end thereof:

On April 9, 2026, AI Day1 tendered all of its shares of Common Stock pursuant to the tender offer by Servier Detroit Inc. to purchase all of the issued and outstanding shares of Common Stock for $21.50 per share in cash, upon the terms and subject to the conditions described in the Offer to Purchase and related Letter of Transmittal filed with the SEC on Schedule TO on March 26, 2026.

**Item 5. Interest in Securities of the Issuer**

**(a)**
Item 5 of the Schedule 13D is hereby amended and restated as follows:

The responses of each of the Reporting Persons with respect to Rows 11, 12, and 13 of the cover pages of this Schedule 13D that relate to the aggregate number and percentage of Common Stock (including but not limited to footnotes to such information) are incorporated herein by reference.

The responses of each of the Reporting Persons with respect to Rows 7, 8, 9, and 10 of the cover pages of this Schedule 13D that relate to the number of Common Stock as to which each of the persons or entities referenced in Item 2 above has sole or shared power to vote or to direct the vote of and sole or shared power to dispose of or to direct the disposition of (including but not limited to footnotes to such information) are incorporated herein by reference.

**(b)**
12,929,322 shares of Common Stock and Warrants to purchase 827,586 shares of Common Stock are owned directly by AI Day1 and may be deemed to be beneficially owned by AIH, AIM and Mr. Blavatnik because (i) AIH indirectly controls all of the outstanding voting interests in AI Day1, (ii) AIM controls AIH and (iii) Mr. Blavatnik controls AIM and controls a majority of the outstanding voting interests in AIH. Each of the Reporting Persons (other than AI Day1), and each of their affiliated entities and the officers, partners, members and managers thereof, disclaims beneficial ownership of these securities.

**(c)**
The following transactions in the Issuer's securities have been effected by Reporting Persons within the 60 days prior to this filing: The information set forth in Item 3 of this Schedule 13D is incorporated by reference herein.

### SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** AI Day1 LLC

**Signature:** /s/ Alejandro Moreno

**Name/Title:** By: Access Industries Management, LLC, its Manager; its Executive Vice President/Alejandro Moreno

**Date:** 04/13/2026

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** Access Industries Holdings LLC

**Signature:** /s/ Alejandro Moreno

**Name/Title:** By: Access Industries Management, LLC, its Manager; its Executive Vice President/Alejandro Moreno

**Date:** 04/13/2026

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** Access Industries Management, LLC

**Signature:** /s/ Alejandro Moreno

**Name/Title:** By: Executive Vice President/Alejandro Moreno

**Date:** 04/13/2026

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** Len Blavatnik

**Signature:** *

**Name/Title:** Len Blavatnik

**Date:** 04/13/2026