# EDGAR Filing Document

**Accession Number:** 0002068530
**File Stem:** 0001104659-25-096741
**Filing Date:** 2025-10
**Character Count:** 19752
**Document Hash:** a378810669c7e7a4a8a8858ba2530342
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-096741.hdr.sgml**: 20251003

**ACCESSION NUMBER**: 0001104659-25-096741

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13G

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20251003

**DATE AS OF CHANGE**: 20251003

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** X4 Pharmaceuticals, Inc
- **CENTRAL INDEX KEY:** 0001501697
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 273181608
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90199
- **FILM NUMBER:** 251375051

**BUSINESS ADDRESS:**
- **STREET 1:** 61 NORTH BEACON STREET
- **STREET 2:** 4TH FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02134
- **BUSINESS PHONE:** 857-529-8300

**MAIL ADDRESS:**
- **STREET 1:** 61 NORTH BEACON STREET
- **STREET 2:** 4TH FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02134

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Arsanis, Inc.
- **DATE OF NAME CHANGE:** 20100920
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Coastlands Capital LP
- **CENTRAL INDEX KEY:** 0002068530

**ORGANIZATION NAME:**
- **EIN:** 333553930
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G

**BUSINESS ADDRESS:**
- **STREET 1:** 601 CALIFORNIA STREET, SUITE 1210
- **CITY:** SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94108
- **BUSINESS PHONE:** (415) 249-1280

**MAIL ADDRESS:**
- **STREET 1:** 601 CALIFORNIA STREET, SUITE 1210
- **CITY:** SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94108

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## SCHEDULE 13G

### Under the Securities Exchange Act of 1934

**Issuer:** X4 Pharmaceuticals, Inc.

**Title of Class of Securities:** Common Stock, par value $0.001 per share

**CUSIP Number:** 98420X202

**Date of Event Which Requires Filing of this Statement:** 10/03/2025

**Check the appropriate box to designate the rule pursuant to which this Schedule is filed:**

- [x] Rule 13d-1(b)

- [x] Rule 13d-1(c)

- [ ] Rule 13d-1(d)

---

| 1. | Names of Reporting Persons<br>Coastlands Capital LP | Names of Reporting Persons<br>Coastlands Capital LP |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>DE | Citizenship or Place of Organization<br>DE |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>2491638.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>2491638.00 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>9.99% | Percent of Class Represented by Amount in Row (9)<br>9.99% |
| 12. | Type of Reporting Person (See Instructions)<br>IA, PN | Type of Reporting Person (See Instructions)<br>IA, PN |

**Comment for Type of Reporting Person:** The calculation of the beneficial ownership of the Reporting Persons is based on (i) 22,449,689 shares of Common Stock issued and outstanding as of August 13, 2025, as reported by the Issuer in its Registration Statement on Form S-3 filed with the Securities and Exchange Commission on September 10, 2025, and (ii) 2,491,638 shares of Common Stock issuable upon the exercise of pre-funded warrants held by the Reporting Persons, which reflects the beneficial ownership limitation of 9.99%.

---

| 1. | Names of Reporting Persons<br>Coastlands Capital Partners LP | Names of Reporting Persons<br>Coastlands Capital Partners LP |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>DE | Citizenship or Place of Organization<br>DE |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>2491638.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>2491638.00 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>9.99% | Percent of Class Represented by Amount in Row (9)<br>9.99% |
| 12. | Type of Reporting Person (See Instructions)<br>PN | Type of Reporting Person (See Instructions)<br>PN |

**Comment for Type of Reporting Person:** The calculation of the beneficial ownership of the Reporting Persons is based on (i) 22,449,689 shares of Common Stock issued and outstanding as of August 13, 2025, as reported by the Issuer in its Registration Statement on Form S-3 filed with the Securities and Exchange Commission on September 10, 2025, and (ii) 2,491,638 shares of Common Stock issuable upon the exercise of pre-funded warrants held by the Reporting Persons, which reflects the beneficial ownership limitation of 9.99%.

---

| 1. | Names of Reporting Persons<br>Coastlands Capital GP LLC | Names of Reporting Persons<br>Coastlands Capital GP LLC |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>DE | Citizenship or Place of Organization<br>DE |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>2491638.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>2491638.00 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>9.99% | Percent of Class Represented by Amount in Row (9)<br>9.99% |
| 12. | Type of Reporting Person (See Instructions)<br>OO | Type of Reporting Person (See Instructions)<br>OO |

**Comment for Type of Reporting Person:** The calculation of the beneficial ownership of the Reporting Persons is based on (i) 22,449,689 shares of Common Stock issued and outstanding as of August 13, 2025, as reported by the Issuer in its Registration Statement on Form S-3 filed with the Securities and Exchange Commission on September 10, 2025, and (ii) 2,491,638 shares of Common Stock issuable upon the exercise of pre-funded warrants held by the Reporting Persons, which reflects the beneficial ownership limitation of 9.99%.

---

| 1. | Names of Reporting Persons<br>Coastlands Capital LLC | Names of Reporting Persons<br>Coastlands Capital LLC |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>DE | Citizenship or Place of Organization<br>DE |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>2491638.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>2491638.00 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>9.99% | Percent of Class Represented by Amount in Row (9)<br>9.99% |
| 12. | Type of Reporting Person (See Instructions)<br>HC, OO | Type of Reporting Person (See Instructions)<br>HC, OO |

**Comment for Type of Reporting Person:** The calculation of the beneficial ownership of the Reporting Persons is based on (i) 22,449,689 shares of Common Stock issued and outstanding as of August 13, 2025, as reported by the Issuer in its Registration Statement on Form S-3 filed with the Securities and Exchange Commission on September 10, 2025, and (ii) 2,491,638 shares of Common Stock issuable upon the exercise of pre-funded warrants held by the Reporting Persons, which reflects the beneficial ownership limitation of 9.99%.

---

| 1. | Names of Reporting Persons<br>Matthew D. Perry | Names of Reporting Persons<br>Matthew D. Perry |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [x] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>X1 | Citizenship or Place of Organization<br>X1 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>2491638.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>0.00 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>2491638.00 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>2491638.00 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>9.99% | Percent of Class Represented by Amount in Row (9)<br>9.99% |
| 12. | Type of Reporting Person (See Instructions)<br>HC, IN | Type of Reporting Person (See Instructions)<br>HC, IN |

**Comment for Type of Reporting Person:** The calculation of the beneficial ownership of the Reporting Persons is based on (i) 22,449,689 shares of Common Stock issued and outstanding as of August 13, 2025, as reported by the Issuer in its Registration Statement on Form S-3 filed with the Securities and Exchange Commission on September 10, 2025, and (ii) 2,491,638 shares of Common Stock issuable upon the exercise of pre-funded warrants held by the Reporting Persons, which reflects the beneficial ownership limitation of 9.99%.

---

**Item 1(a). Name of Issuer:**
X4 Pharmaceuticals, Inc.

**Item 1(b). Address of Issuer's Principal Executive Offices:**
61 North Beacon Street, 4th Floor Boston, MA, 02134

**Item 2(a). Name of Person Filing:**
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")
Matthew D. Perry

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, the Partnership, Coastlands GP and the General Partner. The reporting persons are filing this Schedule 13G 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 13G 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 13G.

**Item 2(b). Address of Principal Business Office:**
601 California Street, Suite 1210, San Francisco, CA 94108

**Item 2(c). Citizenship:**
See Item 4 of the cover sheet for each reporting person.

**Item 2(d). Title of Class of Securities:**
Common Stock, par value $0.001 per share

**Item 2(e). CUSIP Number:**
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) [x] 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) [x] 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:**

Coastlands:  2,491,638
Partnership:  2,491,638
General Partner:  2,491,638
Coastlands GP:  2,491,638
Matthew D. Perry:  2,491,638

**(b) Percent of class:**

Coastlands:  9.99%
Partnership:  9.99%
General Partner:  9.99%
Coastlands GP:  9.99%
Matthew D. Perry:  9.99%

**(c) Number of shares as to which the person has:**

**(i) Sole power to vote or to direct the vote:**

Coastlands:  0
Partnership:  0
General Partner:  0
Coastlands GP:  0
Matthew D. Perry:  0

**(ii) Shared power to vote or to direct the vote:**

Coastlands:  2,491,638
Partnership:  2,491,638
General Partner:  2,491,638
Coastlands GP:  2,491,638
Matthew D. Perry:  2,491,638

**(iii) Sole power to dispose or to direct the disposition of:**

Coastlands:  0
Partnership:  0
General Partner:  0
Coastlands GP:  0
Matthew D. Perry:  0

**(iv) Shared power to dispose or to direct the disposition of:**

Coastlands:  2,491,638
Partnership:  2,491,638
General Partner:  2,491,638
Coastlands GP:  2,491,638
Matthew D. Perry:  2,491,638

**Item 5. Ownership of Five Percent or Less of a Class.**

[x] If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following.

**Item 6. Ownership of More than 5 Percent on Behalf of Another Person.**

The Partnership holds the shares of Common Stock issuable upon exercise of pre-funded warrants, for the benefit of its investors and has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, shares of Common Stock, including shares of Common Stock issuable upon exercise of pre-funded warrants.

**Item 7. Identification and Classification of the Subsidiary**

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. Certification:**

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.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above 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.

**Coastlands Capital LP**

**Date:** 10/03/2025

**By:** /s/ Mark Shamia

**Name & Title:** Chief Operating Officer of the General Partner, Coastlands Capital LLC

**Coastlands Capital Partners LP**

**Date:** 10/03/2025

**By:** /s/ Mark Shamia

**Name & Title:** Chief Operating Officer of the General Partner, Coastlands Capital GP LLC

**Coastlands Capital GP LLC**

**Date:** 10/03/2025

**By:** /s/ Mark Shamia

**Name & Title:** Chief Operating Officer

**Coastlands Capital LLC**

**Date:** 10/03/2025

**By:** /s/ Mark Shamia

**Name & Title:** Chief Operating Officer

**Matthew D. Perry**

**Date:** 10/03/2025

**By:** /s/ Matthew D. Perry

**Name & Title:** Reporting person