13D Filings
Day One Biopharmaceuticals, Inc.
DAWN
Amendment
Ownership

12.52%

Total Shares

12,929,322

Issuer CIK

1845337

Event Date

Apr 8, 2026

Accepted

Apr 13, 2026, 05:06 PM

Reporting Persons (4)
Joint Filing

This is a joint filing. The reported shares may overlap between reporting persons and should not be summed.

NameType% of ClassAggregateSole VotingShared Voting
AI Day1 LLC
Other
12.52%12,929,32212,929,3220
Access Industries Holdings LLC
Other
12.52%12,929,322012,929,322
Access Industries Management, LLC
Other
12.52%12,929,322012,929,322
Len Blavatnik
Individual
12.52%12,929,322012,929,322
Disclosure Items (3)

Security Title

Common Stock, par value $0.0001 per share

Issuer Name

Day One Biopharmaceuticals, Inc.

Issuer Address

1800 Sierra Point Parkway, Brisbane, CA, 94005

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.

Percentage of Class

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.

Number of Shares

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.

Transactions

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.

Shareholders

Not applicable.

Date of 5% Ownership

Not applicable.