Tovorafenib (DAY101) Clinical Trials and Designations - Tovorafenib (DAY101) received FDA Breakthrough Therapy Designation for relapsed pLGG and FDA Rare Pediatric Disease Designation (PRV Eligible) for pLGG[10] - FIREFLY-1, a pivotal Phase 2 trial of Tovorafenib in relapsed or progressive pLGG, showed a 64% ORR (Overall Response Rate) in RANO-evaluable patients (n=22)[21] - The clinical benefit rate (CBR) in the FIREFLY-1 trial was 91%[25] - The median time to response in the FIREFLY-1 trial was 2.8 months[25] - FIREFLY-2/LOGGIC is a pivotal Phase 3 trial of Tovorafenib in newly diagnosed pLGG, with first patient dosing expected in Q4 2022[5, 33] Safety and Tolerability of Tovorafenib - In the FIREFLY-1 trial, 28% of patients required dose modifications due to treatment-related AEs[25] - The majority (96%) of treatment-emergent AEs were grade 1 or 2[25] - The most common treatment-related AEs (Any Grade) were Blood creatine phosphokinase increased (72%), Hair color changes (68%), and Rash (52%)[24] Market and Financial Information - Day One Biopharmaceuticals projected cash runway into 2025[5, 49] - As of September 30, 2022, Day One Biopharmaceuticals had $374.3 million in cash, cash equivalents, and short-term investments[50] - For the nine months ended September 30, 2022, R&D expense was $59.6 million, G&A expense was $44.6 million, and the net loss was $102.1 million[50] Tovorafenib and Pimasertib Combination - FIRELIGHT-1 is evaluating the combination of Tovorafenib (DAY101) and Pimasertib, with the first patient dosed in May 2022[10, 49]

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2022 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-40431 DAY ONE BIOPHARMACEUTICALS, INC. (Exact Name of Registrant as Specified in its Charter) Delaware 83-2415215 (State or ...

Targeted Therapies for People of All Ages August 2022 June 2022 Disclaimer This presentation and the accompanying oral commentary contain forward-looking statements that are based on our management's beliefs and assumptions and on information currently available to our management. Forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified. In some cases, you can identify forward-looking statements by terminology such as "may," "will," "shoul ...

[PART I. FINANCIAL INFORMATION](index=4&type=section&id=PART%20I.%20FINANCIAL%20INFORMATION) This section provides the company's unaudited interim condensed consolidated financial statements and management's discussion and analysis for the period [Item 1. Interim Condensed Consolidated Financial Statements (Unaudited)](index=4&type=section&id=Item%201.%20Interim%20Condensed%20Consolidated%20Financial%20Statements%20(Unaudited)) This section presents the company's unaudited condensed consolidated financial statements for the quarterly period ended June 30, 2022, including balance sheets, statements of operations, comprehensive loss, changes in stockholders' equity, and cash flows, along with detailed notes [Condensed Consolidated Balance Sheets](index=4&type=section&id=Condensed%20Consolidated%20Balance%20Sheets) The balance sheet as of June 30, 2022, shows a significant increase in total assets, primarily driven by a rise in cash and cash equivalents from financing activities, with total stockholders' equity also increasing Condensed Consolidated Balance Sheet Highlights (in thousands) | Account | June 30, 2022 | December 31, 2021 | | :--- | :--- | :--- | | **Assets** | | | | Cash and cash equivalents | $388,877 | $284,309 | | Total current assets | $402,503 | $289,368 | | Total assets | $404,047 | $289,821 | | **Liabilities & Stockholders' Equity** | | | | Total liabilities | $13,416 | $8,673 | | Total stockholders' equity | $390,631 | $281,148 | | Total liabilities and stockholders' equity | $404,047 | $289,821 | [Condensed Consolidated Statements of Operations](index=5&type=section&id=Condensed%20Consolidated%20Statements%20of%20Operations) The company reported a significantly higher net loss for the three and six months ended June 30, 2022, compared to 2021, primarily due to substantial growth in R&D and G&A expenses Statement of Operations Summary (in thousands, except per share data) | Metric | Three Months Ended June 30, 2022 | Three Months Ended June 30, 2021 | Six Months Ended June 30, 2022 | Six Months Ended June 30, 2021 | | :--- | :--- | :--- | :--- | :--- | | Research and development | $22,560 | $9,914 | $37,563 | $22,547 | | General and administrative | $14,159 | $5,525 | $26,904 | $8,990 | | Loss from operations | ($36,719) | ($15,439) | ($64,467) | ($31,537) | | Net loss | ($36,530) | ($15,473) | ($64,277) | ($31,575) | | Net loss per share | ($0.60) | ($5.04) | ($1.08) | ($10.81) | [Condensed Consolidated Statements of Cash Flows](index=8&type=section&id=Condensed%20Consolidated%20Statements%20of%20Cash%20Flows) For the six months ended June 30, 2022, the company experienced a net cash outflow from operating activities, offset by significant cash inflow from financing activities, resulting in a substantial net increase in cash Cash Flow Summary for Six Months Ended June 30 (in thousands) | Activity | 2022 | 2021 | | :--- | :--- | :--- | | Net cash used in operating activities | ($51,350) | ($23,149) | | Net cash used in investing activities | ($6,012) | ($8,000) | | Net cash provided by financing activities | $161,930 | $297,417 | | **Net increase in cash and cash equivalents** | **$104,568** | **$266,268** | [Notes to Condensed Consolidated Financial Statements](index=9&type=section&id=Notes%20to%20Condensed%20Consolidated%20Financial%20Statements) These notes provide crucial details on the company's formation, IPO, significant accounting policies, and financial instruments, including license agreements, equity-based compensation, and financing activities - In June 2022, the company completed a follow-on offering, selling **11,500,000 shares** of common stock for net proceeds of approximately **$161.6 million**[86](index=86&type=chunk) - A milestone payment of **$2.5 million** was made to Merck KGaA in the second quarter of 2022 related to the first dosing of a patient in a clinical trial for a product containing pimasertib[66](index=66&type=chunk) - In July 2022, the company entered into an agreement to develop a companion diagnostic for tovorafenib (DAY101), which includes potential milestone payments of up to **$15.0 million**[110](index=110&type=chunk) - As of June 30, 2022, there was **$70.0 million** of unrecognized compensation cost related to unvested equity awards, expected to be recognized over a weighted-average period of approximately **2.9 years**[104](index=104&type=chunk) [Management's Discussion and Analysis of Financial Condition and Results of Operations](index=24&type=section&id=Item%202.%20Management's%20Discussion%20and%20Analysis%20of%20Financial%20Condition%20and%20Results%20of%20Operations) Management provides an overview of the company's business, focusing on its clinical-stage pipeline led by tovorafenib (DAY101), analyzing the significant increase in operating expenses and net loss, and detailing its strong liquidity position [Overview](index=24&type=section&id=Overview) Day One is a clinical-stage biopharmaceutical company focused on developing targeted therapies, with its lead candidate, tovorafenib (DAY101), in a pivotal Phase 2 trial for pediatric low-grade glioma (pLGG), with promising initial data - The company's lead product candidate, tovorafenib (DAY101), is an oral, brain-penetrant, highly-selective pan-RAF kinase inhibitor[112](index=112&type=chunk) - The pivotal Phase 2 trial (FIREFLY-1) for pediatric patients with relapsed or progressive low-grade glioma (pLGG) completed enrollment in its registrational arm in **May 2022**[112](index=112&type=chunk) - Initial data from FIREFLY-1 in **June 2022** demonstrated an overall response rate (ORR) of **64%** and a clinical benefit rate (CBR) of **91%** in the first **22 evaluable patients**[113](index=113&type=chunk) - The company anticipates reporting topline data from the FIREFLY-1 trial in **Q1 2023** and submitting an NDA to the FDA in the **first half of 2023**[113](index=113&type=chunk) [Results of Operations](index=29&type=section&id=Results%20of%20Operations) The company's operating expenses and net loss increased significantly in the three and six months ended June 30, 2022, primarily due to higher R&D costs from clinical trial and manufacturing activities, and increased G&A expenses from headcount growth and public company operations Comparison of Operating Expenses (in thousands) | Expense Category | Three Months Ended June 30, 2022 | Three Months Ended June 30, 2021 | Change ($) | Change (%) | | :--- | :--- | :--- | :--- | :--- | | Research and development | $22,560 | $9,914 | $12,646 | 127.6% | | General and administrative | $14,159 | $5,525 | $8,634 | 156.3% | | **Total operating expenses** | **$36,719** | **$15,439** | **$21,280** | **137.8%** | - The increase in **Q2 2022 R&D expenses** was driven by a **$7.9 million** rise in third-party clinical trial and manufacturing costs and a **$5.3 million** increase in personnel-related expenses[140](index=140&type=chunk) - The increase in **Q2 2022 G&A expenses** was primarily due to **$4.0 million** in employee compensation from headcount growth and **$4.4 million** in legal, insurance, and professional services[141](index=141&type=chunk) [Liquidity and Capital Resources](index=31&type=section&id=Liquidity%20and%20Capital%20Resources) The company significantly strengthened its financial position through a June 2022 follow-on offering, raising net proceeds of $161.6 million, and expects its current cash to fund operations into 2025 - As of **June 30, 2022**, the company had **$388.9 million** in cash and cash equivalents and an accumulated deficit of **$191.8 million**[149](index=149&type=chunk) - Management believes existing cash will be sufficient to fund operating expenses and capital expenditure requirements into **2025**[149](index=149&type=chunk)[160](index=160&type=chunk) - In **June 2022**, the company completed a follow-on offering with net proceeds of approximately **$161.6 million** and also established a **$150.0 million** at-the-market (ATM) offering program[147](index=147&type=chunk) [Quantitative and Qualitative Disclosures About Market Risk](index=35&type=section&id=Item%203.%20Quantitative%20and%20Qualitative%20Disclosures%20About%20Market%20Risk) The company states that as a smaller reporting company, it is not required to provide the information requested under this item - As a smaller reporting company, Day One is not required to provide quantitative and qualitative disclosures about market risk[169](index=169&type=chunk) [Controls and Procedures](index=35&type=section&id=Item%204.%20Controls%20and%20Procedures) Management concluded that the company's disclosure controls and procedures were effective as of June 30, 2022, with no material changes to internal control over financial reporting during the quarter - Management concluded that the company's disclosure controls and procedures were effective as of **June 30, 2022**[170](index=170&type=chunk) - There were no changes in internal control over financial reporting during the quarter ended **June 30, 2022**, that have materially affected, or are reasonably likely to materially affect, internal controls[171](index=171&type=chunk) [PART II. OTHER INFORMATION](index=36&type=section&id=PART%20II.%20OTHER%20INFORMATION) This section covers other important disclosures including legal proceedings, risk factors, equity sales, and exhibits [Legal Proceedings](index=36&type=section&id=Item%201.%20Legal%20Proceedings) The company reports that it is not currently a party to any legal proceedings that, in management's opinion, would have a material adverse effect on its business - The company is not presently a party to any legal proceedings that would have a material adverse effect on its business[174](index=174&type=chunk) [Risk Factors](index=36&type=section&id=Item%201A.%20Risk%20Factors) This section provides a comprehensive overview of the risks facing the company, including substantial dependence on its lead product candidate, limited operating history, need for additional capital, clinical and regulatory uncertainties, reliance on third parties, and intense competition - **Financial Risks:** The company has a limited operating history, has incurred significant net losses since inception, and expects to incur continued losses, requiring substantial additional capital to finance operations[177](index=177&type=chunk)[181](index=181&type=chunk)[192](index=192&type=chunk) - **Clinical and Commercial Risks:** The company is substantially dependent on the success of its lead product candidate, tovorafenib (DAY101), with clinical trials being expensive, time-consuming, and having uncertain outcomes, potentially impacted by the COVID-19 pandemic[183](index=183&type=chunk)[199](index=199&type=chunk)[227](index=227&type=chunk) - **Third-Party Reliance:** The company relies on third parties for complex manufacturing, which could be subject to delays or disruptions, and for conducting clinical trials[315](index=315&type=chunk)[319](index=319&type=chunk) - **Intellectual Property Risks:** The company's success depends on its ability to obtain and maintain patent protection for its products and technology, which is uncertain and may be challenged by competitors[364](index=364&type=chunk) [Unregistered Sales of Equity Securities and Use of Proceeds](index=97&type=section&id=Item%202.%20Unregistered%20Sales%20of%20Equity%20Securities%20and%20Use%20of%20Proceeds) The company reports no unregistered sales of equity securities for the period and confirms no material change in the planned use of proceeds from its June 2021 Initial Public Offering (IPO) - There were no unregistered sales of equity securities during the period[463](index=463&type=chunk) - The company received net proceeds of approximately **$167.0 million** from its IPO on **June 1, 2021**[465](index=465&type=chunk) - There has been no material change in the planned use of proceeds from the IPO as described in the prospectus[466](index=466&type=chunk) [Defaults Upon Senior Securities](index=98&type=section&id=Item%203.%20Defaults%20Upon%20Senior%20Securities) The company reports that there were no defaults upon senior securities during the period - None[467](index=467&type=chunk) [Mine Safety Disclosures](index=98&type=section&id=Item%204.%20Mine%20Safety%20Disclosures) This item is not applicable to the company - Not applicable[467](index=467&type=chunk) [Other Information](index=98&type=section&id=Item%205.%20Other%20Information) The company reports no other information for this item - None[467](index=467&type=chunk) [Exhibits](index=99&type=section&id=Item%206.%20Exhibits) This section lists the exhibits filed as part of the Quarterly Report on Form 10-Q, including an office lease agreement and certifications from the Principal Executive Officer and Principal Financial Officer - The report includes an exhibit for an office lease dated **April 1, 2022**[468](index=468&type=chunk) - Certifications from the Principal Executive Officer and Principal Financial Officer pursuant to Sections **302** and **906** of the Sarbanes-Oxley Act of **2002** are filed as exhibits[468](index=468&type=chunk)

s 11/2 Day One ₹ BIOPHARMACEUTICALS Targeted Therapies for People of All Ages May 2022 Disclaimer This presentation and the accompanying oral commentary contain forward-looking statements that are based on our management's beliefs and assumptions and on information currently available to our management. Forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified. In some cases, you can identify forward-looking statements by terminology such a ...

[PART I. FINANCIAL INFORMATION](index=4&type=section&id=PART%20I.%20FINANCIAL%20INFORMATION) [Item 1. Interim Consolidated Financial Statements (Unaudited)](index=4&type=section&id=Item%201.%20Interim%20Consolidated%20Financial%20Statements%20(Unaudited)) The unaudited interim consolidated financial statements show a net loss of $27.7 million for Q1 2022 and a cash position of $262.7 million [Condensed Consolidated Balance Sheets](index=4&type=section&id=Condensed%20Consolidated%20Balance%20Sheets) As of March 31, 2022, total assets were $267.8 million, a decrease driven by a reduction in cash and cash equivalents Condensed Consolidated Balance Sheet Highlights (in thousands) | Account | March 31, 2022 | December 31, 2021 | | :--- | :--- | :--- | | **Assets** | | | | Cash and cash equivalents | $262,731 | $284,309 | | Total current assets | $267,368 | $289,368 | | **Total assets** | **$267,779** | **$289,821** | | **Liabilities & Equity** | | | | Total current liabilities | $8,176 | $8,657 | | **Total liabilities** | **$8,176** | **$8,673** | | **Total stockholders' equity** | **$259,603** | **$281,148** | [Condensed Consolidated Statements of Operations and Comprehensive Loss](index=5&type=section&id=Condensed%20Consolidated%20Statements%20of%20Operations%20and%20Comprehensive%20Loss) The company reported a net loss of $27.7 million for Q1 2022, driven by a significant rise in R&D and G&A expenses Condensed Consolidated Statements of Operations (in thousands, except per share data) | Metric | Three Months Ended March 31, 2022 | Three Months Ended March 31, 2021 | | :--- | :--- | :--- | | Research and development | $15,003 | $12,632 | | General and administrative | $12,745 | $3,454 | | **Total operating expenses** | **$27,748** | **$16,086** | | Loss from operations | $(27,748) | $(16,086) | | **Net loss** | **$(27,747)** | **$(16,101)** | | Net loss per share, basic and diluted | $(0.48) | $(2.58) | [Condensed Consolidated Statements of Cash Flows](index=7&type=section&id=Condensed%20Consolidated%20Statements%20of%20Cash%20Flows) Net cash used in operating activities was $21.6 million for Q1 2022, a significant increase from the prior-year period Condensed Consolidated Statements of Cash Flows Highlights (in thousands) | Cash Flow Activity | Three Months Ended March 31, 2022 | Three Months Ended March 31, 2021 | | :--- | :--- | :--- | | Net cash used in operating activities | $(21,563) | $(9,743) | | Net cash used in investing activities | $(15) | $(8,000) | | Net cash provided by financing activities | $0 | $128,885 | | **Net (decrease) increase in cash** | **$(21,578)** | **$111,142** | | Cash and cash equivalents, end of period | $262,731 | $154,870 | [Notes to Condensed Consolidated Financial Statements](index=8&type=section&id=Notes%20to%20Condensed%20Consolidated%20Financial%20Statements) The notes detail the company's clinical-stage focus, key licensing agreements, and significant events like its 2021 IPO - The company is a clinical-stage biopharmaceutical company focused on developing targeted therapies for genomically-defined cancers, with its lead product candidate being **tovorafenib (DAY101)**[25](index=25&type=chunk) - In June 2021, the company closed its IPO, receiving **net proceeds of $167.0 million** after deducting underwriting discounts and offering costs[26](index=26&type=chunk) - The company entered into a license agreement with Merck KGaA for pimasertib, making an **$8.0 million upfront payment** with potential future milestone payments up to **$367.0 million**[44](index=44&type=chunk) Share-based Compensation Expense (in thousands) | Expense Category | Three Months Ended March 31, 2022 | Three Months Ended March 31, 2021 | | :--- | :--- | :--- | | Research and development | $2,147 | $119 | | General and administrative | $4,055 | $419 | | **Total** | **$6,202** | **$538** | [Management's Discussion and Analysis of Financial Condition and Results of Operations](index=19&type=section&id=Item%202.%20Management's%20Discussion%20and%20Analysis%20of%20Financial%20Condition%20and%20Results%20of%20Operations) Management discusses its clinical development focus, Q1 2022 financial results, and its capital sufficiency into 2024 - The lead product candidate, **tovorafenib (DAY101)**, is in a pivotal Phase 2 trial (FIREFLY-1) for pediatric low-grade glioma (pLGG), with initial data expected in June 2022 and a potential NDA filing in 2023[81](index=81&type=chunk) - The second product candidate, **pimasertib**, is being studied in combination with tovorafenib in the FIRELIGHT-1 Phase 1b/2 trial, which was initiated in March 2022[81](index=81&type=chunk) - As of March 31, 2022, the company had **$262.7 million in cash and cash equivalents**, which is believed to be sufficient to fund operations into 2024[85](index=85&type=chunk) [Results of Operations](index=24&type=section&id=Results%20of%20Operations) Total operating expenses increased 72.5% to $27.7 million in Q1 2022, driven by higher clinical trial and personnel costs Comparison of Operating Expenses (in thousands) | Expense Category | Q1 2022 | Q1 2021 | $ Change | % Change | | :--- | :--- | :--- | :--- | :--- | | Research and development | $15,003 | $12,632 | $2,371 | 18.8% | | General and administrative | $12,745 | $3,454 | $9,291 | 269.0% | | **Total operating expenses** | **$27,748** | **$16,086** | **$11,662** | **72.5%** | Breakdown of R&D Expenses (in thousands) | Expense Type | Q1 2022 | Q1 2021 | | :--- | :--- | :--- | | Third-party CRO, CMO costs | $8,245 | $3,434 | | Acquired technology license costs | $0 | $8,000 | | Employee related expenses | $6,168 | $1,156 | | Other R&D costs | $590 | $42 | | **Total R&D expenses** | **$15,003** | **$12,632** | [Liquidity and Capital Resources](index=25&type=section&id=Liquidity%20and%20Capital%20Resources) The company holds $262.7 million in cash, primarily from its 2021 IPO, which is expected to fund operations into 2024 - The company completed its IPO on June 1, 2021, raising **net proceeds of $167.0 million**[107](index=107&type=chunk) - Cash and cash equivalents totaled **$262.7 million** as of March 31, 2022, which management believes is sufficient to fund operations into 2024[107](index=107&type=chunk)[118](index=118&type=chunk) Summary of Cash Flows (in thousands) | Cash Flow Activity | Three Months Ended March 31, 2022 | Three Months Ended March 31, 2021 | | :--- | :--- | :--- | | Net cash used in operating activities | $(21,563) | $(9,743) | | Net cash used in investing activities | $(15) | $(8,000) | | Net cash provided by financing activities | $0 | $128,885 | [Quantitative and Qualitative Disclosures About Market Risk](index=28&type=section&id=Item%203.%20Quantitative%20and%20Qualitative%20Disclosures%20About%20Market%20Risk) As a smaller reporting company, this disclosure is not required - As a smaller reporting company, Day One Biopharmaceuticals is **not required to provide** quantitative and qualitative disclosures about market risk[127](index=127&type=chunk) [Controls and Procedures](index=28&type=section&id=Item%204.%20Controls%20and%20Procedures) Management concluded that disclosure controls and procedures were effective as of the quarter's end - Management concluded that as of March 31, 2022, the company's disclosure controls and procedures were **effective** at a reasonable assurance level[128](index=128&type=chunk) - **No material changes** to the company's internal control over financial reporting occurred during the quarter ended March 31, 2022[129](index=129&type=chunk) [PART II. OTHER INFORMATION](index=29&type=section&id=PART%20II.%20OTHER%20INFORMATION) [Legal Proceedings](index=29&type=section&id=Item%201.%20Legal%20Proceedings) The company is not currently a party to any material legal proceedings - The company is **not presently a party** to any material legal proceedings[132](index=132&type=chunk) [Risk Factors](index=29&type=section&id=Item%201A.%20Risk%20Factors) The company faces significant risks related to its limited operating history, dependence on its lead product, and clinical trial uncertainties - The company has a **limited operating history**, has incurred significant net losses since inception, and may never achieve profitability[135](index=135&type=chunk)[139](index=139&type=chunk) - The business is **substantially dependent on the success** of its lead product candidate, tovorafenib (DAY101), which has not yet completed a pivotal trial[141](index=141&type=chunk) - The company will require **substantial additional capital** to finance operations and is exposed to risks if it is unable to raise capital when needed[150](index=150&type=chunk) - The **COVID-19 pandemic** could adversely impact business operations, including clinical trials, due to delays in enrollment, site initiation, and potential supply chain disruptions[185](index=185&type=chunk) [Unregistered Sales of Equity Securities and Use of Proceeds](index=90&type=section&id=Item%202.%20Unregistered%20Sales%20of%20Equity%20Securities%20and%20Use%20of%20Proceeds) The company reports no unregistered sales of equity and no material change in the planned use of its IPO proceeds - The company received **net proceeds of approximately $167.0 million** from its IPO on June 1, 2021[424](index=424&type=chunk) - There has been **no material change** in the planned use of proceeds from the IPO[425](index=425&type=chunk) [Defaults Upon Senior Securities](index=91&type=section&id=Item%203.%20Defaults%20Upon%20Senior%20Securities) The company reports no defaults upon senior securities - The company reports **no defaults** upon senior securities[426](index=426&type=chunk) [Mine Safety Disclosures](index=91&type=section&id=Item%204.%20Mine%20Safety%20Disclosures) This item is not applicable to the company - This item is **not applicable** to the company[426](index=426&type=chunk) [Other Information](index=91&type=section&id=Item%205.%20Other%20Information) The company reports no other information for this item - The company reports **no other information** for this item[426](index=426&type=chunk) [Exhibits](index=92&type=section&id=Item%206.%20Exhibits) This section lists all exhibits filed with the quarterly report, including required officer certifications

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2021 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM TO Commission File Number 001-40431 DAY ONE BIOPHARMACEUTICALS, INC. (Exact name of Registrant as specified in its Charter) Delaware 83-2415215 (State or other jur ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2021 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-40431 DAY ONE BIOPHARMACEUTICALS, INC. (Exact Name of Registrant as Specified in its Charter) Delaware 83-2415215 (State or ...

Table of Contents Emerging growth company ☒ UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2021 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-40431 Delaware 83-2415215 (State or other jurisdiction of incorporation or organizat ...