Day One Biopharmaceuticals : Change in Certifying Accountants - Form 8-K

Item 4.01

Changes in Registrant's Certifying Accountants.

(a) Dismissal of Previous Independent Registered Public Accounting Firm

On November 10, 2023, the Audit Committee (the "Audit Committee") of the Board of Directors of Day One Biopharmaceuticals, Inc. (the "Company") dismissed Ernst & Young LLP ("EY") as the Company's independent registered public accounting firm. The dismissal was not related to any disagreements with EY on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure.

The reports of EY on the consolidated financial statements of the Company as of and for the fiscal years ended December 31, 2022 and 2021 did not contain an adverse opinion or a disclaimer of opinion and were not qualified or modified as to uncertainty, audit scope, or accounting principles.

During the fiscal years ended December 31, 2022 and 2021 and during the interim period through November 10, 2023 there were (i) no disagreements within the meaning of Item 304(a)(1)(iv) of Regulation S-Kbetween the Company and EY on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, any of which, if not resolved to EY's satisfaction, would have caused EY to make reference thereto in their reports, and (ii) no "reportable events" within the meaning of Item 304(a)(1)(v) of Regulation S-K.

The Company provided EY with a copy of the disclosures it is making in this Current Report on Form 8-Kand requested that EY furnish the Company with a letter addressed to the Securities and Exchange Commission stating whether it agrees with the statements made herein and, if not, stating the respects in which it does not agree. A copy of such letter provided by EY, dated November 15, 2023, is filed as Exhibit 16.1 to this Current Report on Form 8-K.

(b) Appointment of New Independent Registered Public Accounting Firm

On November 10, 2023, the Audit Committee approved the engagement of PricewaterhouseCoopers LLP ("PwC") as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2023. During the Company's two most recent fiscal years ended December 31, 2022 and 2021, and during the interim period through November 10, 2023, neither the Company nor anyone acting on its behalf consulted with PwC regarding any of the matters described in Items 304(a)(2)(i) and (ii) of Regulation S-K.