X0306 4 2021-06-01 0 0001845337 Day One Biopharmaceuticals, Inc. DAWN 0001863302 AI Day 1 LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK NY 10019 0 0 1 0 0001391297 Access Industries Holdings LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FL NEW YORK NY 10019 0 0 0 1 Affiliate of 10% Owner 0001508226 ACCESS INDUSTRIES MANAGEMENT, LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK NY 10019 0 0 0 1 Affiliate of 10% Owner 0001326628 Blavatnik Len C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FL NEW YORK NY 10019 0 0 0 1 Affiliate of 10% Owner Common Stock 2021-06-01 4 C 0 8502776 A 8502776 D Common Stock 2021-06-01 4 P 0 875000 16.00 A 9377776 D Series A Redeemable Convertible Preferred Stock 2021-06-01 4 C 0 7761380 0.00 D Common Stock 7761380 0 D Series B Redeemable Convertible Preferred Stock 2021-06-01 4 C 0 741396 0.00 D Common Stock 741396 0 D Each share of Series A Redeemable Convertible Preferred Stock automatically converted into one share of common stock of Day One Biopharmaceuticals, Inc. (the "Issuer") immediately prior to the completion of the Issuer's initial public offering and had no expiration date. Each share of Series B Redeemable Convertible Preferred Stock automatically converted into one share of common stock of the Issuer immediately prior to the completion of the Issuer's initial public offering and had no expiration date. The securities reported are held directly by AI Day 1 LLC and may be deemed to be beneficially owned by Access Industries Holdings LLC ("AIH"), Access Industries Management, LLC ("AIM") and Len Blavatnik because AIH indirectly controls all of the outstanding voting interests in AI Day 1 LLC, AIM controls AIH and Mr. Blavatnik controls AIM and holds a majority of the outstanding voting interests in AIH. AIH, AIM and Mr. Blavatnik each disclaims beneficial ownership of these securities, except to the extent of its or his pecuniary interest therein, and this form shall not be construed as an admission that any such reporting person is the beneficial owner of any of the securities reported on this form. Represents securities purchased in the Issuer's initial public offering. /s/ Alejandro Moreno for AI Day 1 LLC 2021-06-03 /s/ Alejandro Moreno for Access Industries Holdings LLC 2021-06-03 /s/ Alejandro Moreno for Access Industries Management, LLC 2021-06-03 /s/ Alejandro Moreno as Attorney-in-Fact for Mr. Blavatnik 2021-06-03