Vanguard Group (SNDX) discloses 7.16% beneficial ownership in Syndax

Rhea-AI Filing Summary

The Vanguard Group filed an amended Schedule 13G reporting its beneficial ownership of Syndax Pharmaceuticals common stock as of 12/31/2025. Vanguard reports beneficial ownership of 6,230,334 shares, representing 7.16% of the outstanding common stock. It has no sole voting or dispositive power, with 702,989 shares subject to shared voting power and 6,230,334 shares subject to shared dispositive power. The filing states the securities are held in the ordinary course of business and not for the purpose of changing or influencing control of Syndax. Vanguard notes that its clients have rights to dividends and sale proceeds, with no single client holding more than 5% of the class.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Syndax Pharmaceuticals Inc

(Name of Issuer)

Common Stock

(Title of Class of Securities)

87164F105

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. 87164F105

1

Names of Reporting Persons

The Vanguard Group

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

PENNSYLVANIA

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 702,989.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,230,334.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,230,334.00

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)

7.16 %

12

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person: On January 12, 2026, The Vanguard Group, Inc. went through an internal realignment. As of that date, The Vanguard Group, Inc. no longer performs portfolio management services or administers proxy voting. In accordance with SEC Release No. 34-39538 (January 12, 1998), The Vanguard Group, Inc. anticipates that certain subsidiaries or business divisions of subsidiaries of The Vanguard Group, Inc., that currently have, or are deemed to have, beneficial ownership with The Vanguard Group, Inc., will report beneficial ownership separately (on a disaggregated basis) from The Vanguard Group, Inc. in reliance on such release. These subsidiaries and/or business divisions pursue the same investment strategies as previously pursued by The Vanguard Group, Inc. prior to the realignment.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Syndax Pharmaceuticals Inc
(b)	Address of issuer's principal executive offices: 35 Gatehouse Drive, Building D, 3rd Floor, Waltham, MA, 02451
Item 2.
(a)	Name of person filing: The Vanguard Group
(b)	Address or principal business office or, if none, residence: 100 Vanguard Blvd., Malvern, PA 19355
(c)	Citizenship: PA
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 87164F105
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: 6230334
(b)	Percent of class: 7.16 %
(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: 702989
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: 6230334
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. The Vanguard Group, Inc.'s clients, including investment companies registered under the Investment Company Act of 1940 and other managed accounts, have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities reported herein. No one other person's interest in the securities reported herein is more than 5%.
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 acquired and are held in the ordinary course of business and 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.

The Vanguard Group

Signature:	Ashley Grim
Name/Title:	Head of Global Fund Administration
Date:	01/30/2026

FAQ

What ownership stake does The Vanguard Group report in SNDX?

The Vanguard Group reports beneficial ownership of 6,230,334 Syndax shares, or 7.16% of the common stock. This reflects its aggregate position as of December 31, 2025, across client accounts it manages, reported on an amended Schedule 13G.

How much voting power does Vanguard have in Syndax Pharmaceuticals (SNDX)?

Vanguard reports no sole voting power and shared voting power over 702,989 shares of Syndax. It also reports shared dispositive power over 6,230,334 shares, meaning voting and sale decisions are generally exercised jointly under its investment management arrangements.

Why did The Vanguard Group file this amended Schedule 13G for SNDX?

The amended Schedule 13G updates Vanguard’s beneficial ownership of more than 5% of Syndax’s common stock. The filing confirms the holdings are in the ordinary course of business and not intended to change or influence control of the company.

Do Vanguard’s clients have rights to Syndax (SNDX) dividends and sale proceeds?

Yes, Vanguard states its clients have rights to receive dividends and sale proceeds from the reported Syndax shares. These clients include registered investment companies and other managed accounts, and no single client’s interest exceeds 5% of the class.

What change did Vanguard disclose about its internal structure in this filing?

Vanguard notes an internal realignment effective January 12, 2026, after which it no longer performs portfolio management or proxy voting. Certain subsidiaries or divisions are expected to report beneficial ownership separately on a disaggregated basis while pursuing the same investment strategies.

Is Vanguard seeking to influence control of Syndax Pharmaceuticals through this stake?

No, Vanguard certifies the Syndax securities were acquired and are held in the ordinary course of business. It explicitly states they are not held for changing or influencing control, nor in connection with any transaction having that purpose or effect.