Vanguard reports 5.05% stake in Syndax

Syndax Pharmaceuticals Inc ownership disclosure: Vanguard Capital Management reports beneficial ownership of 4,457,143 shares of Common Stock, representing 5.05% of the class as of 03/31/2026.

Rhea-AI Filing Summary

Syndax Pharmaceuticals Inc ownership disclosure: Vanguard Capital Management reports beneficial ownership of 4,457,143 shares of Common Stock, representing 5.05% of the class as of 03/31/2026. The filing states Vanguard has sole dispositive power over 4,457,143 shares and sole voting power over 634,564 shares. The report explains these holdings include securities held for Vanguard funds and managed accounts and names affiliate divisions exercising voting or dispositive power.

Insights

Institutional Ownership Analyst

Vanguard holds a >5% stake in Syndax as of 03/31/2026

Vanguard Capital Management reports beneficial ownership of 4,457,143 shares, equal to 5.05% of outstanding common stock. The filing attributes sole dispositive power to Vanguard and lists affiliated investment divisions that may exercise voting or dispositive authority.

Investor implications depend on whether Vanguard funds increase or decrease holdings; subsequent beneficial ownership filings would show any material changes.

Key Figures

Beneficial ownership: 4,457,143 shares Percent of class: 5.05% Sole voting power: 634,564 shares +3 more

6 metrics

Beneficial ownership 4,457,143 shares as of 03/31/2026

Percent of class 5.05% ownership percentage reported

Sole voting power 634,564 shares shares with sole voting power

Sole dispositive power 4,457,143 shares shares with sole dispositive power

Record date 03/31/2026 date used for ownership calculation

Signature date 04/30/2026 date filing was signed

Key Terms

beneficially owned, sole dispositive power, sole voting power, Schedule 13G

4 terms

beneficially owned regulatory

"this reflects the securities beneficially owned, or deemed to be beneficially owned"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole dispositive power regulatory

"Sole power to dispose or to direct the disposition of: 4457143"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

sole voting power regulatory

"Sole power to vote or to direct the vote: 634,564"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

Schedule 13G regulatory

"Item 1. (a) Name of issuer: Syndax Pharmaceuticals Inc"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stake does Vanguard hold in Syndax Pharmaceuticals (SNDX)?

Vanguard reports beneficial ownership of 4,457,143 shares, equal to 5.05% of Syndax common stock as of 03/31/2026. This ownership reflects holdings across Vanguard funds and managed accounts, per the filing.

Who has voting and dispositive power for Vanguard's SNDX shares?

The filing states Vanguard Capital Management has sole dispositive power over 4,457,143 shares and sole voting power over 634,564 shares. Affiliates and business divisions may exercise additional voting or dispositive authority.

When was the Schedule 13G for SNDX signed and filed?

The Schedule 13G is dated for holdings as of 03/31/2026 and was signed on 04/30/2026 by Ashley Grim, Head of Global Fund Administration, representing Vanguard Capital Management.

Does Vanguard report any other person with >5% interest in SNDX?

The filing states no other single person's interest in the reported securities exceeds 5%. Vanguard notes holdings include shares held for Vanguard-registered funds and managed accounts.

What entities are listed as affiliates in Vanguard's SNDX filing?

The filing names affiliates including Vanguard Asset Management Limited, Vanguard Fiduciary Trust Company, Vanguard Global Advisers, LLC, and Vanguard Investments Australia Ltd. as part of the beneficial-ownership explanation.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 04/30/2026 - 01:53 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Syndax Pharmaceuticals Inc

(Name of Issuer)

Common Stock

(Title of Class of Securities)

87164F105

(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): 87164F105

1

Names of Reporting Persons

Vanguard Capital Management

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 634,564.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 4,457,143.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,457,143.00

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)

5.05 %

12

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person: In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by Vanguard Capital Management LLC and the following affiliates of Vanguard Capital Management LLC or business divisions of such affiliates: Vanguard Asset Management Limited, Vanguard Fiduciary Trust Company, Vanguard Global Advisers, LLC and Vanguard Investments Australia Ltd. This Schedule 13G includes securities held by Vanguard funds, or sleeves thereof, over which Vanguard Capital Management LLC exercises dispositive power, in addition to securities held by clients over which the affiliates or business divisions of such affiliates indicated above exercise dispositive and/or voting power. This Schedule 13G does not include securities, if any, beneficially owned by other subsidiaries or affiliates of Vanguard Capital Management LLC, or business divisions of such subsidiaries, whose ownership of securities is disaggregated from that of the reporting business unit in accordance with such release.

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: Vanguard Capital Management
(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 Number(s): 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: 4457143
(b)	Percent of class: 5.05 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 634564
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 4457143
	(iv) Shared power to dispose or to direct the disposition of: 0
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. Vanguard Capital Management, 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.

Vanguard Capital Management

Signature:	Ashley Grim
Name/Title:	Head of Global Fund Administration
Date:	04/30/2026