Zenas BioPharma: Wellington reports 10.07% stake

Wellington-affiliated investment advisers report passive beneficial ownership of just over 10% of Zenas BioPharma’s common stock held in client accounts.

Rhea-AI Filing Summary

For Zenas BioPharma, Inc. (ZBIO), a group of Wellington investment entities filed a Schedule 13G reporting passive beneficial ownership of Zenas common stock. They report aggregate beneficial ownership of 6,566,134 shares of common stock, representing 10.07% of the outstanding class.

The Wellington entities report no sole voting or dispositive power, but shared voting power over 6,308,474 shares and shared dispositive power over 6,566,134 shares, held in client accounts advised by various Wellington investment advisers. The filing notes that clients, including Vanguard Health Care Fund, have rights to dividends or sale proceeds, but no individual client is known to hold more than five percent of the class.

Key Figures

Beneficial ownership: 6,566,134 shares Percent of class owned: 10.07% Shared voting power: 6,308,474 shares +4 more

7 metrics

Beneficial ownership 6,566,134 shares Aggregate shares of Zenas BioPharma common stock reported as beneficially owned by Wellington entities

Percent of class owned 10.07% Percentage of Zenas BioPharma common stock class reported as beneficially owned

Shared voting power 6,308,474 shares Shares over which Wellington reporting entities have shared power to vote or direct the vote

Shared dispositive power 6,566,134 shares Shares over which Wellington reporting entities have shared power to dispose or direct the disposition

Sole voting power 0 shares Shares over which Wellington reporting entities have sole power to vote

Sole dispositive power 0 shares Shares over which Wellington reporting entities have sole power to dispose

Wellington Management Company LLP beneficial ownership percentage 9.9% Percent of Zenas BioPharma common stock reported on the Wellington Management Company LLP cover page

Key Terms

beneficially owned, shared voting power, dispositive power, Schedule 13G, +2 more

6 terms

beneficially owned financial

"Amount beneficially owned: See the responses to Item 9 on the attached cover pages."

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.

shared voting power financial

"Shared Voting Power 6,308,474.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

dispositive power financial

"Shared Dispositive Power 6,566,134.00"

Dispositive power is the authority to decide the final outcome of an asset, legal claim, contract, or corporate action — in effect the power to dispose of or resolve something. For investors it matters because whoever holds that authority can determine who gets paid, who controls an asset or vote, and how risks and returns are allocated; think of it like holding the key that lets you lock in the winner or loser in a deal.

Schedule 13G regulatory

"The securities as to which this Schedule is filed are owned of record"

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.

investment advisers financial

"The securities as to which this Schedule is filed are owned of record by clients of one or more investment advisers"

parent holding company financial

"The securities as to which this Schedule is filed by Wellington Management Group LLP, as parent holding company"

FAQ

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

How much of Zenas BioPharma (ZBIO) stock do the Wellington entities report owning?

They report beneficial ownership of 6,566,134 shares of Zenas BioPharma common stock, representing 10.07% of the outstanding class. These shares are held in client accounts managed by Wellington-affiliated investment advisers.

What voting and dispositive power do the Wellington entities report over ZBIO shares?

They report 0 shares with sole voting or dispositive power, 6,308,474 shares with shared voting power, and 6,566,134 shares with shared dispositive power over Zenas BioPharma common stock.

Which Wellington entities are listed as reporting persons for Zenas BioPharma (ZBIO)?

The reporting persons are Wellington Management Group LLP, Wellington Group Holdings LLP, Wellington Investment Advisors Holdings LLP, and Wellington Management Company LLP, together with related Wellington investment advisers identified in the filing.

Are the Zenas BioPharma (ZBIO) shares held directly by Wellington or by its clients?

The securities are owned of record by clients of one or more Wellington investment advisers. Those clients have the right to receive dividends and sale proceeds, while the Wellington group reports beneficial ownership due to its advisory and control relationships.

Does any single Wellington client hold more than 5% of Zenas BioPharma (ZBIO)?

The filing states that no client is known to have the right to receive or direct dividends or sale proceeds with respect to more than five percent of the class, except that Vanguard Health Care Fund is identified as an exception.

What is the nature of Wellington’s filing on Zenas BioPharma (ZBIO)?

The document is a Schedule 13G, indicating a passive beneficial ownership position. Wellington Management Group LLP files as a parent holding company of certain holding companies and investment advisers that manage client accounts holding Zenas shares.

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

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Available on EDGAR 09/08/2026 - 07:39 AM Accepted by SEC EDGAR 09/08/2026 - 07:39 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Zenas Biopharma, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

98937L105

(CUSIP Number)

08/31/2026

(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): 98937L105

1

Names of Reporting Persons

Wellington Management Group LLP

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

MASSACHUSETTS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 6,308,474.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,566,134.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,566,134.00

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)

10.1 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

CUSIP Number(s): 98937L105

1

Names of Reporting Persons

Wellington Group Holdings LLP

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 6,308,474.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,566,134.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,566,134.00

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)

10.1 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

CUSIP Number(s): 98937L105

1

Names of Reporting Persons

Wellington Investment Advisors Holdings LLP

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 6,308,474.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,566,134.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,566,134.00

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)

10.1 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

CUSIP Number(s): 98937L105

1

Names of Reporting Persons

Wellington Management Company LLP

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 6,300,635.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,438,573.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,566,134.00

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)

9.9 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Zenas Biopharma, Inc.
(b)	Address of issuer's principal executive offices: 1000 Winter St, North Building, Suite 1200, Waltham MA
Item 2.
(a)	Name of person filing: Wellington Management Group LLP Wellington Group Holdings LLP Wellington Investment Advisors Holdings LLP Wellington Management Company LLP
(b)	Address or principal business office or, if none, residence: c/o Wellington Management Company LLP, 280 Congress Street, Boston MA 02210
(c)	Citizenship: Wellington Management Group LLP - Massachusetts Wellington Group Holdings LLP - Delaware Wellington Investment Advisors Holdings LLP - Delaware Wellington Management Company LLP - Delaware
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 98937L105
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: See the responses to Item 9 on the attached cover pages.
(b)	Percent of class: 10.07 %
(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: See the responses to Item 6 on the attached cover pages.
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: See the responses to Item 8 on the attached cover pages.
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 securities as to which this Schedule is filed are owned of record by clients of one or more investment advisers identified in Item 7 directly or indirectly owned by Wellington Management Group LLP. Those clients have the right to receive, or the power to direct the receipt of, dividends from, or the proceeds from the sale of, such securities. No such client is known to have such right or power with respect to more than five percent of this class of securities, except as follows: Vanguard Health Care Fund
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. Pursuant to the instructions in Item 7 of Schedule 13G, the following lists the identity and Item 3 classification of each relevant entity that beneficially owns shares of the security class being reported on this Schedule 13G. Wellington Group Holdings LLP - HC Wellington Investment Advisors LLP - HC Wellington Management Global Holdings, Ltd. - HC One or more of the following investment advisers (the "Wellington Investment Advisers"): Wellington Management Company LLP - IA Wellington Management Canada LLC - IA Wellington Management Singapore Pte Ltd - IA Wellington Management Hong Kong Ltd - IA Wellington Management International Ltd - IA Wellington Management Japan Pte Ltd - IA Wellington Management Australia Pty Ltd - IA The securities as to which this Schedule is filed by Wellington Management Group LLP, as parent holding company of certain holding companies and the Wellington Investment Advisers, are owned of record by clients of the Wellington Investment Advisers. Wellington Investment Advisors Holdings LLP controls directly, or indirectly through Wellington Management Global Holdings, Ltd., the Wellington Investment Advisers. Wellington Investment Advisors Holdings LLP is owned by Wellington Group Holdings LLP. Wellington Group Holdings LLP is owned by Wellington Management Group LLP.
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.

Wellington Management Group LLP

Signature:	Matthew Revell
Name/Title:	Compliance Manager
Date:	09/08/2026

Wellington Group Holdings LLP

Signature:	Matthew Revell
Name/Title:	Compliance Manager
Date:	09/08/2026

Wellington Investment Advisors Holdings LLP

Signature:	Matthew Revell
Name/Title:	Compliance Manager
Date:	09/08/2026

Wellington Management Company LLP

Signature:	Matthew Revell
Name/Title:	Compliance Manager
Date:	09/08/2026