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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549 |
SCHEDULE 13G
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UNDER THE SECURITIES EXCHANGE ACT OF 1934
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(Amendment No. 4)*
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Day One Biopharmaceuticals, Inc. (Name of Issuer) |
COMMON STOCK, $0.0001 PAR VALUE (Title of Class of Securities) |
(CUSIP Number) |
03/31/2026 (Date of Event Which Requires Filing of this Statement) |
| Check the appropriate box to designate the rule pursuant to which this Schedule is filed: |
 Rule 13d-1(b)
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 Rule 13d-1(c)
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| Rule 13d-1(d)
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SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Fund XI, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates XI, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates XI, LLC | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
OO |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Opportunity Fund I, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates Opportunity I, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates Opportunity I, LLC | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
OO |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Opportunity Fund II, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates Opportunity II, L.P. | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
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| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
PN |
SCHEDULE 13G
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| CUSIP No. |
| 1 | Names of Reporting Persons
Atlas Venture Associates Opportunity II, LLC | ||||||||
| 2 | Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
| ||||||||
| 3 | Sec Use Only | ||||||||
| 4 | Citizenship or Place of Organization
DELAWARE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 9 | Aggregate Amount Beneficially Owned by Each Reporting Person
0.00 | ||||||||
| 10 | Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
| ||||||||
| 11 | Percent of class represented by amount in row (9)
0.0 % | ||||||||
| 12 | Type of Reporting Person (See Instructions)
OO |
SCHEDULE 13G
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| Item 1. | ||
| (a) | Name of issuer:
Day One Biopharmaceuticals, Inc. | |
| (b) | Address of issuer's principal executive offices:
1800 Sierra Point Parkway, Suite 200, BRISBANE, CA, 94005. | |
| Item 2. | ||
| (a) | Name of person filing:
This Schedule 13G is filed by (i) Atlas Venture Fund XI, L.P., a Delaware limited partnership ("Atlas XI"), (ii) Atlas Venture Associates XI, L.P., a Delaware limited partnership ("AVA XI LP"), (iii) Atlas Venture Associates XI, LLC, a Delaware limited liability company ("AVA XI LLC" and together with Atlas XI and AVA XI LP, the "Fund XI Reporting Persons"), (iv) Atlas Venture Opportunity Fund I, L.P., a Delaware limited partnership ("AVO I"), (v) Atlas Venture Associates Opportunity I, L.P., a Delaware limited partnership ("AVAO LP"), (vi) Atlas Venture Associates Opportunity I, LLC, a Delaware limited liability company ("AVAO LLC" and together with AVO I and AVAO LP, the "Opportunity Fund Reporting Persons"), (vii) Atlas Venture Opportunity Fund II, L.P., a Delaware limited partnership ("AVO II"), (viii) Atlas Venture Associates Opportunity II, L.P., a Delaware limited partnership ("AVAO II LP") and (ix) Atlas Venture Associates Opportunity II, LLC, a Delaware limited liability company ("AVAO II LLC" and together with AVO II and AVAO II LP, the "Opportunity Fund II Reporting Persons" and together with the Fund XI Reporting Persons and Opportunity Fund Reporting Persons, the "Reporting Persons"). | |
| (b) | Address or principal business office or, if none, residence:
300 Technology Square, 8th Floor
Cambridge, Massachusetts 02139 | |
| (c) | Citizenship:
Each of Atlas XI, AVA XI LP, AVO I, AVAO LP, AVO II and AVAO II LP is a Delaware limited partnership.
Each of AVA XI LLC, AVAO LLC and AVAO II LLC is a Delaware limited liability company. | |
| (d) | Title of class of securities:
COMMON STOCK, $0.0001 PAR VALUE | |
| (e) | CUSIP No.:
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| Item 3. | If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a: | |
| (a) | Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
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| (b) | Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
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| (c) | Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
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| (d) | Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
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| (e) | An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
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| (f) | An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
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| (g) | A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
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| (h) | A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
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| (i) | A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
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| (j) | A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution: | |
| (k) | Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
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| Item 4. | Ownership | |
| (a) | Amount beneficially owned:
0 | |
| (b) | Percent of class:
0 %
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| (c) | Number of shares as to which the person has:
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| (i) Sole power to vote or to direct the vote:
0 | ||
| (ii) Shared power to vote or to direct the vote:
0 | ||
| (iii) Sole power to dispose or to direct the disposition of:
0 | ||
| (iv) Shared power to dispose or to direct the disposition of:
0 | ||
| Item 5. | Ownership of 5 Percent or Less of a Class. | |
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Ownership of 5 percent or less of a class
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| Item 6. | Ownership of more than 5 Percent on Behalf of Another Person. | |
Not Applicable
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| Item 7. | Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person. | |
Not Applicable
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| Item 8. | Identification and Classification of Members of the Group. | |
Not Applicable
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| Item 9. | Notice of Dissolution of Group. | |
Not Applicable
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| Item 10. | Certifications: |
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. |
| SIGNATURE | |
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
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Exhibit Information
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JOINT FILING AGREEMENT |
Exhibit 99.1
JOINT FILING AGREEMENT
In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Day One Biopharmaceuticals, Inc. and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.
Date: May 15, 2026
| Atlas Venture Fund XI, L.P. | |
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| By: | Atlas Venture Associates XI, L.P., its general partner |
| By: | Atlas Venture Associates XI, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
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| Atlas Venture Associates XI, L.P. | |
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| By: | Atlas Venture Associates XI, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
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| Atlas Venture Associates XI, LLC | |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
| Atlas Venture Opportunity Fund I, L.P. | |
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| By: | Atlas Venture Associates Opportunity I, L.P., its general partner |
| By: | Atlas Venture Associates Opportunity I, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
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| Atlas Venture Associates Opportunity I, L.P. | |
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| By: | Atlas Venture Associates Opportunity I, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
| Atlas Venture Associates Opportunity I, LLC | |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
| Atlas Venture Opportunity Fund II, L.P. | |
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| By: | Atlas Venture Associates Opportunity II, L.P., its general partner |
| By: | Atlas Venture Associates Opportunity II, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
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| Atlas Venture Associates Opportunity II, L.P. | |
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| By: | Atlas Venture Associates Opportunity II, LLC, its general partner |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |
| Atlas Venture Associates Opportunity II, LLC | |
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| By: /s/ Ommer Chohan | |
| Name: | Ommer Chohan |
| Title: | Chief Financial Officer |