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In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F6","text":"The option vests as to 1/48th of the total shares monthly, commencing February 15, 2025, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":90000,"derivative":{"exercise_price":8.99,"expiration_date":"2035-01-14","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":7,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004562,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"disposition_to_issuer","planned":false,"acquired":false,"shares":90000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F2","text":"On October 7, 2025, the Issuer's Board of Directors approved an option repricing (the \"Repricing\") whereby the Reporting Person's options were repriced on November 6, 2025 (the \"Effective Date\") with a new exercise price of $8.99 (if lower than the original exercise price), the closing price on Nasdaq as of the Effective Date.  In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F6","text":"The option vests as to 1/48th of the total shares monthly, commencing February 15, 2025, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":0,"derivative":{"exercise_price":11.87,"expiration_date":"2035-01-14","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":6,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004561,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"grant","planned":false,"acquired":true,"shares":90000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F2","text":"On October 7, 2025, the Issuer's Board of Directors approved an option repricing (the \"Repricing\") whereby the Reporting Person's options were repriced on November 6, 2025 (the \"Effective Date\") with a new exercise price of $8.99 (if lower than the original exercise price), the closing price on Nasdaq as of the Effective Date.  In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F5","text":"The option vests as to 1/48th of the total shares monthly, commencing February 5, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":90000,"derivative":{"exercise_price":8.99,"expiration_date":"2034-01-04","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":5,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004560,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"disposition_to_issuer","planned":false,"acquired":false,"shares":90000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F2","text":"On October 7, 2025, the Issuer's Board of Directors approved an option repricing (the \"Repricing\") whereby the Reporting Person's options were repriced on November 6, 2025 (the \"Effective Date\") with a new exercise price of $8.99 (if lower than the original exercise price), the closing price on Nasdaq as of the Effective Date.  In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F5","text":"The option vests as to 1/48th of the total shares monthly, commencing February 5, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":0,"derivative":{"exercise_price":14.44,"expiration_date":"2034-01-04","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":4,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004559,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"grant","planned":false,"acquired":true,"shares":90000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F2","text":"On October 7, 2025, the Issuer's Board of Directors approved an option repricing (the \"Repricing\") whereby the Reporting Person's options were repriced on November 6, 2025 (the \"Effective Date\") with a new exercise price of $8.99 (if lower than the original exercise price), the closing price on Nasdaq as of the Effective Date.  In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F4","text":"The option vests as to 1/48th of the total shares monthly, commencing February 17, 2023, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":90000,"derivative":{"exercise_price":8.99,"expiration_date":"2033-01-16","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004558,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"disposition_to_issuer","planned":false,"acquired":false,"shares":90000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F2","text":"On October 7, 2025, the Issuer's Board of Directors approved an option repricing (the \"Repricing\") whereby the Reporting Person's options were repriced on November 6, 2025 (the \"Effective Date\") with a new exercise price of $8.99 (if lower than the original exercise price), the closing price on Nasdaq as of the Effective Date.  In order to exercise the repriced options at the new exercise price, the Reporting Person is required to remain in service with the Issuer through the Retention Period; provided that the additional premium payment will not be required if the Reporting Person's service to the Issuer is terminated by reason of death or Disability (as defined in the Company's 2021 Equity Incentive Plan (\"the Plan\"))."},{"field":"kind","element":"transactionCoding","label":"F3","text":"(Continued from Footnote 2)  The \"Retention Period\" commenced on the Effective Date and ends upon the earliest of (i) the 12-month anniversary of the Effective Date and (ii) a Corporate Transaction (as defined in the Plan).  All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F4","text":"The option vests as to 1/48th of the total shares monthly, commencing February 17, 2023, subject to the Reporting Person's provision of service to the Issuer on each vesting date."}],"balance_after":0,"derivative":{"exercise_price":23.41,"expiration_date":"2033-01-16","underlying":"Common Stock","underlying_shares":90000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1004557,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Stock Option (right to buy Common Stock)","published_at":"2025-11-07T23:00:51.000Z","date":"2025-11-06","kind":"grant","planned":false,"acquired":true,"shares":309000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"The option vests as to 100% of the total shares on November 6, 2026, subject to the Reporting Person's provision of service to the Issuer on such vesting date."}],"balance_after":309000,"derivative":{"exercise_price":8.99,"expiration_date":"2032-10-30","underlying":"Common Stock","underlying_shares":309000},"source":{"system":"sec-edgar","filing":"0001744507-25-000004","document":"form4-11072025_111147.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1744507/000174450725000004/form4-11072025_111147.xml","form_type":"4"}},{"id":1061112,"issuer":{"id":51180,"kind":"organization","name":"Day One Biopharmaceuticals, Inc.","symbol":"DAWN"},"owners":[{"id":15598,"kind":"person","name":"Dubow Adam","position":1,"cik":"0001744507","reported_name":"Dubow Adam","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Gen Counsel & Secretary"}}],"security":"Restricted Stock Unit (RSU)","published_at":"2025-08-19T23:38:03.000Z","date":"2025-08-15","kind":"exercise","planned":false,"acquired":false,"shares":3687,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_price","element":"conversionOrExercisePrice","label":"F1","text":"Each Restricted Stock Unit (\"RSU\") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F6","text":"The RSUs will vest as to 1/16th of the total award in quarterly installments on February 15, May 15, August 15 and November 15, subject to the Reporting Person's provision of service to the Issuer on each vesting date."},{"field":"derivative.expiration_date","element":"expirationDate","label":"F5","text":"RSUs do not expire; 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