[SCHEDULE 13D] X4 Pharmaceuticals, Inc. SEC Filing

Rhea-AI Filing Summary

Coastlands Capital and affiliated persons report acquiring a 9.99% beneficial ownership stake in X4 Pharmaceuticals (XFOR) following an August 2025 financing. The Reporting Persons hold an aggregate position equal to 2,479,645 shares of Common Stock on a fully‑diluted basis subject to a beneficial ownership blocker. Coastlands purchased a pre‑funded warrant exercisable for up to 7,047,216 shares for $9,999,999.50 and directly holds 107,500 shares purchased on August 12, 2025 for $1.7074 per share. The August 2025 Financing issued 11,040,776 shares and pre‑funded warrants to investors at $1.42 per share and $1.419 per pre‑funded warrant, respectively, and closed August 13, 2025. The Reporting Persons used working capital to fund their purchase, have registration rights for resale, and note Board changes at the Company including termination of the CEO and CFO and appointments of an Executive Chairman, new CFO and new President.

Insights

Securities Analyst

TL;DR: Coastlands acquired a near‑10% stake via a pre‑funded warrant and market purchases, with blocking limits to cap ownership below 10%.

The Reporting Persons collectively report beneficial ownership of 9.99% (2,479,645 shares) driven by a pre‑funded warrant exercisable for 7,047,216 shares and direct holdings of 107,500 shares. The pre‑funded warrant has a $0.001 exercise price but contains a Beneficial Ownership Blocker preventing exercise that would exceed 9.99% ownership. Coastlands paid $9,999,999.50 for the pre‑funded warrant and used working capital for purchases. A resale registration rights agreement was obtained, supporting liquidity for the acquired securities. The filing is routine for a financing participant but is material due to the size of the position and related governance changes disclosed by the issuer.

Corporate Governance Specialist

TL;DR: The filing discloses board leadership changes concurrent with the financing and documents investor protections and ownership limits.

The Schedule 13D notes the issuer's board approved termination of the CEO and CFO and appointed an Executive Chairman, a new CFO and a new President concurrent with the August 2025 Financing. The Reporting Persons reserve the right to engage with management and the board but state no current plans beyond the financing. The registration rights and pre‑funded warrant terms (including the Beneficial Ownership Blocker and Fundamental Transaction provisions) are documented and incorporated by reference, indicating negotiated investor protections and transferability considerations typical in private placement financings.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

X4 Pharmaceuticals, Inc

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

98420X202

(CUSIP Number)

Mark Shamia
Coastlands Capital LP, 601 California Street, Suite 1210
San Francisco, CA, 94108
(415) 249-1282

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

08/11/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 98420X202

1

Name of reporting person

Coastlands Capital LP

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 2,479,645.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 2,479,645.00

11

Aggregate amount beneficially owned by each reporting person

2,479,645.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.99 %

14

Type of Reporting Person (See Instructions)

IA, PN

Comment for Type of Reporting Person:

Percentage calculated based on 11,408,357 shares of Common Stock outstanding on August 4, 2025, as reported in the Form 10-Q filed by the Issuer for the quarter ended June 30, 2025, plus 11,040,776 shares of Common Stock issued in a private placement transaction, which closed on August 13, 2025. The securities exclude shares of Common Stock issuable upon exercise of a pre-funded warrant in excess of the beneficial ownership limitation of 9.99%.

SCHEDULE 13D

CUSIP No. 98420X202

1

Name of reporting person

Coastlands Capital Partners LP

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 2,479,645.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 2,479,645.00

11

Aggregate amount beneficially owned by each reporting person

2,479,645.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.99 %

14

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person:

Percentage calculated based on 11,408,357 shares of Common Stock outstanding on August 4, 2025, as reported in the Form 10-Q filed by the Issuer for the quarter ended June 30, 2025, plus 11,040,776 shares of Common Stock issued in a private placement transaction, which closed on August 13, 2025. The securities exclude shares of Common Stock issuable upon exercise of a pre-funded warrant in excess of the beneficial ownership limitation of 9.99%.

SCHEDULE 13D

CUSIP No. 98420X202

1

Name of reporting person

Coastlands Capital GP LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 2,479,645.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 2,479,645.00

11

Aggregate amount beneficially owned by each reporting person

2,479,645.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.99 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

Percentage calculated based on 11,408,357 shares of Common Stock outstanding on August 4, 2025, as reported in the Form 10-Q filed by the Issuer for the quarter ended June 30, 2025, plus 11,040,776 shares of Common Stock issued in a private placement transaction, which closed on August 13, 2025. The securities exclude shares of Common Stock issuable upon exercise of a pre-funded warrant in excess of the beneficial ownership limitation of 9.99%.

SCHEDULE 13D

CUSIP No. 98420X202

1

Name of reporting person

Coastlands Capital LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 2,479,645.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 2,479,645.00

11

Aggregate amount beneficially owned by each reporting person

2,479,645.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.99 %

14

Type of Reporting Person (See Instructions)

HC, OO

Comment for Type of Reporting Person:

Percentage calculated based on 11,408,357 shares of Common Stock outstanding on August 4, 2025, as reported in the Form 10-Q filed by the Issuer for the quarter ended June 30, 2025, plus 11,040,776 shares of Common Stock issued in a private placement transaction, which closed on August 13, 2025. The securities exclude shares of Common Stock issuable upon exercise of a pre-funded warrant in excess of the beneficial ownership limitation of 9.99%.

SCHEDULE 13D

CUSIP No. 98420X202

1

Name of reporting person

Matthew D. Perry

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 2,479,645.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 2,479,645.00

11

Aggregate amount beneficially owned by each reporting person

2,479,645.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.99 %

14

Type of Reporting Person (See Instructions)

IN, HC

Comment for Type of Reporting Person:

Percentage calculated based on 11,408,357 shares of Common Stock outstanding on August 4, 2025, as reported in the Form 10-Q filed by the Issuer for the quarter ended June 30, 2025, plus 11,040,776 shares of Common Stock issued in a private placement transaction, which closed on August 13, 2025. The securities exclude shares of Common Stock issuable upon exercise of a pre-funded warrant in excess of the beneficial ownership limitation of 9.99%.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.001 per share
(b)	Name of Issuer: X4 Pharmaceuticals, Inc
(c)	Address of Issuer's Principal Executive Offices: 61 North Beacon Street, 4th Floor, Boston, MASSACHUSETTS , 02134.
Item 2.	Identity and Background
(a)	This Schedule 13D is being filed jointly by Coastlands Capital LP, a Delaware limited partnership ("Coastlands"), Coastlands Capital Partners LP, a Delaware limited partnership (the "Partnership"), Coastlands Capital GP LLC, a Delaware limited liability company (the "General Partner"), Coastlands Capital LLC, a Delaware limited liability company ("Coastlands GP" and together with Coastlands, the Partnership and the General Partner, the "Coastlands Entities"), and Matthew D. Perry (together with the Coastlands Entities, the "Reporting Persons"). The joint filing agreement of the Reporting Persons is attached as Exhibit 99.1 to this Schedule 13D. Coastlands and the General Partner are the investment adviser and general partner, respectively, of the Partnership. Coastlands GP is the general partner of Coastlands. Mr. Perry is the control person of Coastlands, Coastlands GP and the General Partner. The Reporting Persons are filing this Schedule 13D jointly, but not as members of a group, and each disclaims membership in a group. Each Reporting Person also disclaims beneficial ownership of Common Stock except to the extent of that person's pecuniary interest therein. In addition, the filing of this Schedule 13D on behalf of the Partnership should not be construed as an admission that it is, and it disclaims that it is, a beneficial owner, as defined in Rule 13d-3 under the Act, of any Common Stock covered by this Schedule 13D.
(b)	The principal business address for each of the Reporting Persons is 601 California Street, Suite 1210, San Francisco, CA 94108.
(c)	Each of the Coastlands Entities is principally engaged in the business of investment in securities. The principal occupation of Mr. Perry is investment management.
(d)	During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).
(e)	During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violation of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.
(f)	See Item 2(a) hereof for citizenship information for the Coastlands Entities. Mr. Perry is a citizen of the United States.
Item 3.	Source and Amount of Funds or Other Consideration
	On August 11, 2025 and August 12, 2025, the Issuer entered into Securities Purchase Agreements (the "Purchase Agreements") with certain investors identified therein, including Coastlands (collectively, the "Investors"), pursuant to which the Investors purchased from the Issuer an aggregate of 11,040,776 shares of Common Stock, at a purchase price of $1.42 per share, and pre-funded warrants to purchase an aggregate of 48,852,772 shares of Common Stock, at a purchase price of $1.419 per pre-funded warrant (the "August 2025 Financing"). The August 2025 Financing closed on August 13, 2025. In the August 2025 Financing, Coastlands purchased a pre-funded warrant exercisable for 7,047,216 shares of Common Stock for a purchase price of $9,999,999.50. Coastlands used its own working capital to acquire the securities. References to and the description of the Purchase Agreement set forth above in this Item 3 do not purport to be complete and are qualified in their entirety by reference to the full text of the Purchase Agreement, which is attached hereto as Exhibit 99.2 and incorporated by reference herein.
Item 4.	Purpose of Transaction
	Concurrent with the August 2025 Financing, the Issuer's board of directors (the "Board") approved (i) the termination of each of the Chief Executive Officer and Chief Financial Officer of the Company and (ii) the appointment of an Executive Chairman, a new Chief Financial Officer and a new President of the Company. Except as described in this Schedule 13D, the Reporting Persons do not have any present plans or proposals that relate to or would result in any of the actions described in subparagraphs (a) through (j) of Item 4 of Schedule 13D, although, the Reporting Persons, at any time and from time to time, may review, reconsider and change their position and/or change their purpose and/or develop such plans and may seek to influence management or the board of directors of the Company with respect to the business and affairs of the Company and may from time to time consider pursuing or proposing such matters with advisors, the Issuer or other persons.
Item 5.	Interest in Securities of the Issuer
(a)	The information set forth in Items 2, 3 and 6 and on the cover pages of this Schedule 13D is incorporated by reference in its entirety into this Item 5. As of the date hereof, Coastlands directly holds 107,500 shares of Common Stock and a pre-funded warrant exercisable for up to 7,047,216 shares of Common Stock. As a result of the Beneficial Ownership Blocker (as defined below), the Reporting Persons are precluded from exercising the pre-funded warrant into shares of Common Stock to the extent that the Reporting Persons would, after such exercise, collectively beneficially own in excess of 9.99% of the outstanding Common Stock of the Issuer. Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described in Item 2 of this Schedule 13D, the Reporting Persons may be deemed to collectively beneficially own 9.99% of the outstanding Common Stock of the Issuer, representing 2,479,645 shares of Common Stock as of the date hereof. The calculation of the beneficial ownership of the Reporting Persons is based on (i) 11,408,357 shares of Common Stock issued and outstanding as of August 4, 2025, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2025, filed with the Securities and Exchange Commission on August 8, 2025; (ii) 11,040,776 shares of Common Stock issued by the Issuer in the August 2025 Financing; and (iii) 2,372,145 shares of Common Stock issuable upon the exercise of the pre-funded warrant held by the Reporting Persons, which reflects the Beneficial Ownership Blocker.
(b)	See Item 5(a) hereof.
(c)	See Item 3 of this Schedule 13D. On August 12, 2025, the Reporting Persons purchased 107,500 shares of Common Stock in the open market at a price per share of $1.7074, for an aggregate purchase price of $183,545.50.
(d)	Except as otherwise described in this Item 5, no one other than the Reporting Persons has the right to receive, or the power to direct the receipt of, dividends from, or the proceeds from the sale of, any of the Common Stock beneficially owned by the Reporting Persons as described in this Item 5.
(e)	Not applicable.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	Pre-Funded Warrants Exercisability. The pre-funded warrant held by the Reporting Persons is exercisable at any time after its original issuance. Exercise Blocker. Exercise of each pre-funded warrant is prohibited if, as a result of such exercise, the holder, together with its affiliates and other persons whose beneficial ownership would be aggregated with the holder's for purposes of Section 13(d) of the Act, would beneficially own more than 9.99% of the total number of shares of Common Stock then issued and outstanding immediately after giving effect to the exercise (the "Beneficial Ownership Blocker"). Exercise Price. The Reporting Persons hold pre-funded warrants exercisable for up to 7,047,216 shares of Common Stock with an exercise price of $0.001 per share. The exercise price is subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations or reclassifications affecting the Common Stock. Fundamental Transaction. If a Fundamental Transaction (as defined in the pre-funded warrant) occurs while a pre-funded warrant is outstanding, then upon any subsequent exercise of the pre-funded warrant, the holder thereof has the right to receive the same amount and kind of securities, cash or property as such holder would have been entitled to receive upon the occurrence of such Fundamental Transaction if it had been, immediately prior to such Fundamental Transaction, the holder of the number of shares of Common Stock then issuable upon exercise in full of the pre-funded warrant (without regard to any limitations on exercise). Rights as a Stockholder. Except as otherwise provided in the pre-funded warrant or by virtue of the holder's ownership of Common Stock, the holder of a pre-funded warrant does not have the rights or privileges of a holder of Common Stock, including any voting rights, until the holder exercises the pre-funded warrant. References to and the description of the pre-funded warrant set forth in this Item 6 do not purport to be complete and are qualified in their entirety by reference to the form of pre-funded warrant, which is attached hereto as Exhibit 99.3 and incorporated by reference herein. Registration Rights Agreement The Reporting Persons have entered into a resale registration rights agreement with the Issuer in connection with the August 2025 Financing pursuant to which the Issuer agreed to file a registration statement covering the resale, by the Reporting Persons, of certain shares of Common Stock held by the Reporting Persons and to use commercially reasonable efforts to cause such registration statement to remain effective until such time as all such shares of Common Stock have been sold or no longer qualify as registrable securities. References to and the description of the registration rights agreement set forth in this Item 6 do not purport to be complete and are qualified in their entirety by reference to the registration rights agreement, which is attached hereto as Exhibit 99.4 and incorporated by reference herein.
Item 7.	Material to be Filed as Exhibits.
	Exhibit 99.1 Agreement Regarding Joint Filing of Statement on Schedule 13D or 13G Exhibit 99.2 Purchase Agreement (incorporated by reference from Exhibit 10.1 to the Issuer's Current Report on Form 8-K filed with the SEC on August 12, 2025) Exhibit 99.3 Form of Pre-Funded Warrant (incorporated by reference from Exhibit 4.1 to the Issuer's Current Report on Form 8-K filed with the SEC on August 12, 2025) Exhibit 99.4 August 2025 Registration Rights Agreement (incorporated by reference from Exhibit 10.2 to the Issuer's Current Report on Form 8-K filed with the SEC on August 12, 2025)

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.

Coastlands Capital LP

Signature:	/s/ Mark Shamia
Name/Title:	Chief Operating Officer of the General Partner, Coastlands Capital LLC
Date:	08/18/2025

Coastlands Capital Partners LP

Signature:	/s/ Mark Shamia
Name/Title:	Chief Operating Officer of the General Partner, Coastlands Capital GP LLC
Date:	08/18/2025

Coastlands Capital GP LLC

Signature:	/s/ Mark Shamia
Name/Title:	Chief Operating Officer
Date:	08/18/2025

Coastlands Capital LLC

Signature:	/s/ Mark Shamia
Name/Title:	Chief Operating Officer
Date:	08/18/2025

Matthew D. Perry

Signature:	/s/ Matthew D. Perry
Name/Title:	Reporting person
Date:	08/18/2025