BlackRock reports 5.9% stake in X4 Pharmaceuticals

BlackRock, Inc. reports beneficial ownership of common stock of X4 PHARMACEUTICALS INC.

Accepted by SEC EDGAR 07/30/2026 - 11:18 AM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

BlackRock, Inc. reports beneficial ownership of common stock of X4 PHARMACEUTICALS INC. BlackRock holds 5,529,573 shares, representing 5.9% of the outstanding common stock. It has sole voting powersole dispositive power

Various underlying clients and accounts have rights to dividends and sale proceeds from these shares, but no single underlying interest exceeds five percent of X4 PHARMACEUTICALS INC’s total outstanding common stock.

Key Figures

Beneficial ownership: 5,529,573 shares Percent of class: 5.9% Sole voting power: 5,467,295 shares +4 more

7 metrics

Beneficial ownership 5,529,573 shares Common stock of X4 PHARMACEUTICALS INC beneficially owned by BlackRock, Inc.

Percent of class 5.9% Portion of X4 PHARMACEUTICALS INC common stock class held by BlackRock, Inc.

Sole voting power 5,467,295 shares Shares for which BlackRock, Inc. has sole power to vote or direct the vote

Shared voting power 0 shares Shares for which BlackRock, Inc. has shared power to vote or direct the vote

Sole dispositive power 5,529,573 shares Shares for which BlackRock, Inc. has sole power to dispose or direct disposition

Shared dispositive power 0 shares Shares for which BlackRock, Inc. has shared power to dispose or direct disposition

Signature date 07/30/2026 Date Managing Director Spencer Fleming signed the Schedule 13G

Key Terms

beneficially owned, Sole Voting Power, Sole Dispositive Power, Percent of class, +1 more

5 terms

beneficially owned financial

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

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 Voting Power financial

"5 | Sole Voting Power 5,467,295.00 6 | Shared Voting Power 0.00"

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.

Sole Dispositive Power financial

"7 | Sole Dispositive Power 5,529,573.00 8 | Shared Dispositive Power 0.00"

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.

Percent of class financial

"(b) | Percent of class: 5.9 %"

Percent of class is the portion of a specific category of securities—such as a company’s common shares, preferred shares, or a bond series—that takes part in or approves a corporate action (vote, consent, tender, etc.). Investors watch this number because it reveals how much support or opposition exists within that particular shareholder group; like counting how many members of a club back a proposal, it can determine whether a plan passes or how influence is distributed.

Schedule 13G regulatory

"In accordance with SEC Release No. 34-39538 ... this schedule reflects the securities"

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.

How many XFOR shares does BlackRock, Inc. report owning on its Schedule 13G?

BlackRock reports 5,529,573 X4 PHARMACEUTICALS INC (XFOR) common shares as beneficially owned. This position represents 5.9% of the company’s outstanding common stock, giving BlackRock a significant institutional holding in the issuer.

What percentage of X4 PHARMACEUTICALS INC (XFOR) does BlackRock control the vote for?

BlackRock has sole voting power over 5,467,295 X4 PHARMACEUTICALS INC (XFOR) shares. It reports no shared voting power, indicating voting authority is concentrated within BlackRock’s reporting business units for these shares.

What is BlackRock’s dispositive power over XFOR shares in this Schedule 13G?

BlackRock reports sole dispositive power over 5,529,573 X4 PHARMACEUTICALS INC (XFOR) shares. It has no shared dispositive power, meaning only BlackRock’s reporting business units control decisions to sell or otherwise dispose of these shares.

Are any individual BlackRock clients above 5% ownership in X4 PHARMACEUTICALS INC (XFOR)?

No single underlying person has an interest exceeding 5% of X4 PHARMACEUTICALS INC’s common stock. Various persons can receive dividends or sale proceeds, but each holds less than five percent of the total outstanding shares.

Where is X4 PHARMACEUTICALS INC (XFOR) headquartered according to this Schedule 13G?

X4 PHARMACEUTICALS INC’s principal executive offices are at 61 North Beacon Street, 4th Floor, Boston, MA 02134. This address identifies the company’s main business location for regulatory and shareholder communications.

Who signed the Schedule 13G for BlackRock’s XFOR holdings and when?

The Schedule 13G is signed by Spencer Fleming, Managing Director at BlackRock, Inc. The signature is dated 07/30/2026, formalizing the reported beneficial ownership and related authority disclosures as of that date.

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

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

X4 PHARMACEUTICALS INC

(Name of Issuer)

Common Stock

(Title of Class of Securities)

98420X202

(CUSIP Number)

06/30/2026

(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): 98420X202

1

Names of Reporting Persons

BlackRock, Inc.

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 5,467,295.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 5,529,573.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

5,529,573.00

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)

5.9 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

Item 1.
(a)	Name of issuer: X4 PHARMACEUTICALS INC
(b)	Address of issuer's principal executive offices: 61 NORTH BEACON STREET, 4TH FLOOR BOSTON MA 02134
Item 2.
(a)	Name of person filing: BlackRock, Inc. 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 certain business units (collectively, the "Reporting Business Units") of BlackRock, Inc. and its subsidiaries and affiliates. It does not include securities, if any, beneficially owned by other business units whose beneficial ownership of securities are disaggregated from that of the Reporting Business Units in accordance with such release.
(b)	Address or principal business office or, if none, residence: BlackRock, Inc., 50 Hudson Yards New York, NY 10001
(c)	Citizenship: See Item 4 of Cover Page
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 98420X202
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: 5529573
(b)	Percent of class: 5.9 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 5467295
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 5529573
	(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. Various persons have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of the common stock of X4 PHARMACEUTICALS INC. No one person's interest in the common stock of X4 PHARMACEUTICALS INC is more than five percent of the total outstanding common shares.
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. See Exhibit 99
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.

BlackRock, Inc.

Signature:	Spencer Fleming
Name/Title:	Managing Director
Date:	07/30/2026

Exhibit Information

Exhibit 24: Power of Attorney Exhibit 99: Item 7