Day One Biopharmaceuticals (NASDAQ: DAWN) filing shows 0% Atlas ownership

Rhea-AI Filing Summary

Day One Biopharmaceuticals, Inc. Schedule 13G/A amendment shows a group of Atlas Venture entities collectively reporting zero beneficial ownership in the company’s common stock (CUSIP 23954D109). The filing lists multiple Atlas Venture partnerships and LLCs and is signed by Ommer Chohan on behalf of those entities.

Key Figures

Document date: 03/31/2026 Signature date: 05/14/2026 Beneficial ownership: 0 shares +2 more

5 metrics

Document date 03/31/2026 Cover date shown on the amendment

Signature date 05/14/2026 Date signatures by Ommer Chohan were executed

Beneficial ownership 0 shares Amount beneficially owned reported in Item 4(a)

Percent of class 0% Percent of class reported in Item 4(b)

CUSIP 23954D109 Identifier for Day One Biopharmaceuticals common stock

Key Terms

Schedule 13G/A, Beneficial ownership, Joint Filing Agreement

3 terms

Schedule 13G/A regulatory

"Amendment No. 4 ) Day One Biopharmaceuticals, Inc."

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

Beneficial ownership financial

"Item 4. | Ownership (a) | Amount beneficially owned: 0"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

Joint Filing Agreement regulatory

"Exhibit Information JOINT FILING AGREEMENT"

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Accepted by SEC EDGAR 05/14/2026 - 04:19 PM Learn about SEC filing dates

FAQ

What did the Schedule 13G/A filed for DAWN report?

The filing reports that Atlas Venture entities beneficially own 0 shares of Day One Biopharmaceuticals common stock, representing 0% of the class. It identifies multiple Atlas Venture partnerships and LLCs and provides a joint filing agreement signed by Ommer Chohan.

Which Atlas Venture entities are named in the DAWN filing?

Named reporting persons include Atlas Venture Fund XI, L.P., Atlas Venture Associates XI entities, Atlas Venture Opportunity Fund I and II entities, and affiliated LLCs. Each entity’s place of organization is listed as Delaware and the business address is in Cambridge, Massachusetts.

When were the signatures and document date recorded in the filing for DAWN?

The amendment shows a document date of 03/31/2026 on the cover and signature dates of 05/14/2026. Signatures are executed by Ommer Chohan on behalf of the various Atlas Venture reporting entities.

Does the Schedule 13G/A indicate any voting or dispositive power for Atlas Venture in DAWN?

No. The ownership table shows 0 for sole and shared voting power and sole and shared dispositive power, and lists beneficial ownership as 0 shares, representing 0% of the common stock class.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 4)

Day One Biopharmaceuticals, Inc.

(Name of Issuer)

COMMON STOCK, $0.0001 PAR VALUE

(Title of Class of Securities)

23954D109

(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)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

CUSIP Number(s): 23954D109

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:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 0.00

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

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.: 23954D109
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);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(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);
(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).
Item 4.	Ownership
(a)	Amount beneficially owned: 0
(b)	Percent of class: 0 %
(c)	Number of shares as to which the person has:
	(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.
	Ownership of 5 percent or less of a class
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
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
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

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.

Atlas Venture Fund XI, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates XI, L.P., its GP, By: Atlas Venture Associates XI, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates XI, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates XI, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates XI, LLC

Signature:	/s/ Ommer Chohan
Name/Title:	Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Opportunity Fund I, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity I, L.P., its GP, By: Atlas Venture Associates Opportunity I, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates Opportunity I, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity I, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates Opportunity I, LLC

Signature:	/s/ Ommer Chohan
Name/Title:	Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Opportunity Fund II, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity II, L.P., its GP, By: Atlas Venture Associates Opportunity II, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates Opportunity II, L.P.

Signature:	/s/ Ommer Chohan
Name/Title:	By: Atlas Venture Associates Opportunity II, LLC, its GP, By: Ommer Chohan, CFO
Date:	05/14/2026

Atlas Venture Associates Opportunity II, LLC

Signature:	/s/ Ommer Chohan
Name/Title:	Ommer Chohan, CFO
Date:	05/14/2026

Exhibit Information

JOINT FILING AGREEMENT