# EDGAR Filing Document

**Accession Number:** 0001501697
**File Stem:** 0001072613-25-000643
**Filing Date:** 2025-8
**Character Count:** 42437
**Document Hash:** e05932fc5625e549bafd4974e662ce72
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001072613-25-000643.hdr.sgml**: 20250815

**ACCESSION NUMBER**: 0001072613-25-000643

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 3

**FILED AS OF DATE**: 20250815

**DATE AS OF CHANGE**: 20250815

**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 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90199
- **FILM NUMBER:** 251225418

**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:** Growth Equity Opportunities 18 VGE, LLC
- **CENTRAL INDEX KEY:** 0001917895

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 1954 GREENSPRING DRIVE
- **STREET 2:** SUITE 600
- **CITY:** TIMONIUM
- **STATE:** MD
- **ZIP:** 21093
- **BUSINESS PHONE:** 410-842-4000

**MAIL ADDRESS:**
- **STREET 1:** 1954 GREENSPRING DRIVE
- **STREET 2:** SUITE 600
- **CITY:** TIMONIUM
- **STATE:** MD
- **ZIP:** 21093

## Ex-1

**<u>EXHIBIT 1</u>**

**AGREEMENT**

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13D need be filed with respect to the ownership by each of the undersigned of shares of stock of X4 Pharmaceuticals, Inc.

EXECUTED this 15<sup>th</sup> day of August, 2025.

GROWTH EQUITY OPPORTUNITIES 18 VGE, LLC

By: NEA 18 VENTURE GROWTH EQUITY, L.P. Sole Member

By: NEA PARTNERS 18 VGE, L.P. General Partner

By: NEA 18 VGE GP, LLC General Partner

By: <u>\*</u> 

Anthony A. Florence, Jr.

Managing Partner and Co-Chief Executive Officer

By: <u>\*</u> 

Mohamad Makhzoumi

Managing Partner and Co-Chief Executive Officer

NEA 18 VENTURE GROWTH EQUITY, L.P.

By: NEA PARTNERS 18 VGE, L.P. General Partner

By: NEA 18 VGE GP, LLC General Partner

By: <u>\*</u> 

Anthony A. Florence, Jr.

Managing Partner and Co-Chief Executive Officer

By: <u>\*</u> 

Mohamad Makhzoumi

Managing Partner and Co-Chief Executive Officer

NEA PARTNERS 18 VGE, L.P.

By: NEA 18 VGE GP, LLC<br> General Partner

By: <u>\*</u> 

Anthony A. Florence, Jr.

Managing Partner and Co-Chief Executive Officer

By: <u>\*</u> 

Mohamad Makhzoumi

Managing Partner and Co-Chief Executive Officer

NEA 18 VGE GP, LLC

By: <u>\*</u> 

Anthony A. Florence, Jr.

Managing Partner and Co-Chief Executive Officer

By: <u>\*</u> 

Mohamad Makhzoumi

Managing Partner and Co-Chief Executive Officer

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Ali Behbahani

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Carmen Chang

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Anthony A. Florence, Jr.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Mohamad H. Makhzoumi

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Edward T. Mathers

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Scott D. Sandell

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Paul Walker

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<u>\*</u> 

Rick Yang

<u>\*/s/ Zachary Bambach</u> 

Zachary Bambach

As attorney-in-fact

This Agreement relating to Schedule 13D was executed by Zachary Bambach on behalf of the individuals listed above pursuant to a Power of Attorney, a copy of which is attached hereto as Exhibit 2.

## Ex-2

**<u>EXHIBIT 2</u>**

**POWER OF ATTORNEY**

KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints Zachary Bambach, Nicole Hatcher and Stephanie Brecher, and each of them, with full power to act without the others, his or her true and lawful attorney-in-fact, with full power of substitution, to sign any and all instruments, certificates and documents that may be necessary, desirable or appropriate to be executed on behalf of himself as an individual or in his or her capacity as a direct or indirect general partner, director, officer or manager of any partnership, corporation or limited liability company, pursuant to section 13 or 16 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and any and all regulations promulgated thereunder, including, without limitation, Forms 3, 4 and 5 and Schedules 13D and 13G (and any amendments thereto), and to file the same, with all exhibits thereto, and any other documents in connection therewith, with the Securities and Exchange Commission (the "SEC"), including, but not limited to, signing a Form ID for and on behalf of the undersigned and filing such Form ID with the SEC, and with any other entity when and if such is mandated by the Exchange Act or by the Financial Industry Regulatory Authority, granting unto said attorney-in-fact full power and authority to do and perform each and every act and thing necessary, desirable or appropriate, fully to all intents and purposes as he or she might or could do in person, thereby ratifying and confirming all that said attorney-in-fact, or his or her substitutes, may lawfully do or cause to be done by virtue hereof. This power of attorney is perpetual, unless revoked by the undersigned in a signed writing delivered to each of the foregoing attorneys-in-fact.

IN WITNESS WHEREOF, this Power of Attorney has been signed as of the 29th day of February, 2024.

---

| |
|:---|
| /s/ Peter J. Barris |
| Peter J. Barris |
| /s/ Forest Baskett |
| Forest Baskett |
| /s/ Ali Behbahani |
| Ali Behbahani |
| /s/ Ronald D. Bernal |
| Ronald D. Bernal |
| /s/ Ann Bordetsky |
| Ann Bordetsky |
| /s/ Carmen Chang |
| Carmen Chang |
| /s/ Philip Chopin |
| Philip Chopin |
| /s/ Anthony A. Florence, Jr. |
| Anthony A. Florence, Jr. |
| /s/ Jonathan Golden |
| Jonathan Golden |
| /s/ Scott Gottlieb |
| Scott Gottlieb |
| /s/ Mark Hawkins |
| Mark Hawkins |
| /s/ Jeffrey R. Immelt |
| Jeffrey R. Immelt |
| /s/ Aaron Jacobson |
| Aaron Jacobson |
| /s/ Patrick J. Kerins |
| Patrick J. Kerins |
| /s/ Hilarie Koplow-McAdams |
| Hilarie Koplow-McAdams |
| /s/ Vanessa Larco |
| Vanessa Larco |
| /s/ Julio C. Lopez |
| Julio C. Lopez |
| /s/ Tiffany Le |
| Tiffany Le |
| /s/ Mohamad H. Makhzoumi |
| Mohamad H. Makhzoumi |
| /s/ Edward T. Mathers |
| Edward T. Mathers |
| /s/ Gregory Papadopoulos |
| Gregory Papadopoulos |
| /s/ Kavita Patel |
| Kavita Patel |
| /s/ Scott D. Sandell |
| Scott D. Sandell |
| /s/ A. Brooke Seawell |
| A. Brooke Seawell |
| /s/ Peter Sonsini |
| Peter Sonsini |
| /s/ Melissa Taunton |
| Melissa Taunton |
| /s/ Paul E. Walker |
| Paul E. Walker |
| /s/ Rick Yang |
| Rick Yang |

---

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

## SCHEDULE 13D

### Under the Securities Exchange Act of 1934

**(Amendment No. 3)**

**X4 Pharmaceuticals, Inc.**

*(Name of Issuer)*

**Common Stock, par value $0.001 per share**

*(Title of Class of Securities)*

**98420X202**

*(CUSIP Number)*

**Stephanie Brecher**<br>New Enterprise Associates<br>1954 Greenspring Drive, Suite 600<br>Timonium MD 21093<br>(410)842-4000

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

**08/13/2025**

*(Date of Event Which Requires Filing of this Statement)*

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Growth Equity Opportunities 18 VGE, LLC** | Name of reporting person<br>**Growth Equity Opportunities 18 VGE, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**NEA 18 Venture Growth Equity, L.P.** | Name of reporting person<br>**NEA 18 Venture Growth Equity, L.P.** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**NEA Partners 18 VGE, L.P.** | Name of reporting person<br>**NEA Partners 18 VGE, L.P.** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**NEA 18 VGE GP, LLC** | Name of reporting person<br>**NEA 18 VGE GP, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Ali Behbahani** | Name of reporting person<br>**Ali Behbahani** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Carmen Chang** | Name of reporting person<br>**Carmen Chang** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Anthony A. Florence, Jr.** | Name of reporting person<br>**Anthony A. Florence, Jr.** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Mohamad H. Makhzoumi** | Name of reporting person<br>**Mohamad H. Makhzoumi** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Edward T. Mathers** | Name of reporting person<br>**Edward T. Mathers** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Scott D. Sandell** | Name of reporting person<br>**Scott D. Sandell** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Paul Walker** | Name of reporting person<br>**Paul Walker** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **98420X202** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Rick Yang** | Name of reporting person<br>**Rick Yang** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2243658.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2243658.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | Aggregate amount beneficially owned by each reporting person<br>**2243658.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**9.99%** | Percent of class represented by amount in Row (11)<br>**9.99%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**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, MA, 02134

This Amendment No. 3 ("Amendment No. 3") to Schedule 13D amends and supplements the Schedule 13D originally filed on July 19, 2022 (the "Schedule 13D"), Amendment No. 1 thereto filed on December 20, 2022 ("Amendment No. 1") and Amendment No. 2 thereto filed on May 26, 2023 ("Amendment No. 2"), relating to the Common Stock of the Issuer.

Certain terms used but not defined in this Amendment No. 3 have the meanings assigned thereto in the Schedule 13D (and Amendment No. 1 and Amendment No. 2 thereto). Except as specifically provided herein, this Amendment No. 3 does not modify any of the information previously reported on the Schedule 13D (and Amendment No. 1 and Amendment No. 2 thereto).

**Item 4. Purpose of Transaction**

GEO acquired the GEO Shares for investment purposes. Information with respect to the Private Placement set forth in Item 3 above is incorporated herein by reference to the extent responsive to this Item 4.

Subject to the foregoing, depending on market conditions, its continuing evaluation of the business and prospects of the Issuer and other factors, GEO and other Reporting Persons may dispose of or acquire additional shares of the Issuer. Except as set forth above, none of the Reporting Persons has any present plans which relate to or would result in:

(a) The acquisition by any person of additional securities of the Issuer, or the disposition of securities of the Issuer;

(b) An extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries;

(c) A sale or transfer of a material amount of assets of the Issuer or any of its subsidiaries;

(d) Any change in the present board of directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board;

(e) Any material change in the present capitalization or dividend policy of the Issuer;

(f) Any other material change in the Issuer's business or corporate structure;

(g) Changes in the Issuer's charter, bylaws or instruments corresponding thereto or other actions which may impede the acquisition of control of the Issuer by any person;

(h) Causing a class of securities of the Issuer to be delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association;

(i) A class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Securities Exchange Act of 1934; or

(j) Any action similar to any of those enumerated above.

**Item 5. Interest in Securities of the Issuer**

**(a)**
GEO is the record owner of the GEO Shares. As the sole member of GEO, NEA 18 VGE may be deemed to own beneficially the GEO Shares. As the sole general partner of NEA 18 VGE, NEA Partners 18 VGE may be deemed to own beneficially the GEO Shares. As the sole general partner of NEA Partners 18 VGE, NEA 18 VGE LLC may be deemed to own beneficially the GEO Shares. As members of NEA 18 VGE LLC, each of the Managers may be deemed to own beneficially the GEO Shares.

Each Reporting Person disclaims beneficial ownership of the GEO Shares other than those shares which such person owns of record.

The percentage of outstanding Common Stock of the Issuer which may be deemed to be beneficially owned by each Reporting Person is set forth on Line 13 of such Reporting Person's cover sheet. Such percentage was calculated based on 22,459,047 shares of Common Stock, which includes the sum of (i) 11,408,357 shares of Common Stock reported by the Issuer to be outstanding as of August 4, 2025 on the Issuer's Form 10-Q, filed with the SEC on August 8, 2025, (ii) 11,040,776 shares of Common Stock reported to be sold by the Issuer in connection with the Private Placement on the Form 8-K and (iii) the Exercisable Shares.

**(b)**
Regarding the number of shares as to which such person has:
(i) sole power to vote or to direct the vote: See line 7 of cover sheets
(ii) shared power to vote or to direct the vote: See line 8 of cover sheets
(iii) sole power to dispose or to direct the disposition: See line 9 of cover sheets
(iv) shared power to dispose or to direct the disposition: See line 10 of cover sheets.

**(c)**
Except as set forth in Item 3 above, none of the Reporting Persons has effected any transaction in the Common Stock during the last 60 days.

**Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.**

Information with respect to the Private Placement set forth in Item 3 above is incorporated herein by reference to the extent responsive to this Item 6.

In connection with the Private Placement and pursuant to the terms of the Securities Purchase Agreement, on August 11, 2025, the Issuer, GEO and the other investors party to the Securities Purchase Agreement entered into a registration rights agreement (the "Registration Rights Agreement"), pursuant to which the Issuer agreed to provide certain registration rights with respect to the Registrable Securities (as defined in the Registration Rights Agreement) under the Securities Act and the rules and regulations promulgated thereunder, and applicable state securities laws. A copy of the Registration Rights Agreement is attached as Exhibit 10.2 to the Form 8-K and incorporated herein by reference.

### 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.

**Reporting Person:** Growth Equity Opportunities 18 VGE, LLC

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Anthony A. Florence Jr., Managing Partner and Co-Chief Executive Officer

**Date:** 08/15/2025

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.

**Reporting Person:** NEA 18 Venture Growth Equity, L.P.

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Anthony A. Florence Jr., Managing Partner and Co-Chief Executive Officer

**Date:** 08/15/2025

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.

**Reporting Person:** NEA Partners 18 VGE, L.P.

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Anthony A. Florence Jr., Managing Partner and Co-Chief Executive Officer

**Date:** 08/15/2025

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.

**Reporting Person:** NEA 18 VGE GP, LLC

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Anthony A. Florence Jr., Managing Partner and Co-Chief Executive Officer

**Date:** 08/15/2025

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.

**Reporting Person:** Ali Behbahani

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Ali Behbahani

**Date:** 08/15/2025

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.

**Reporting Person:** Carmen Chang

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Carmen Chang

**Date:** 08/15/2025

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.

**Reporting Person:** Anthony A. Florence, Jr.

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Anthony A. Florence, Jr.

**Date:** 08/15/2025

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.

**Reporting Person:** Mohamad H. Makhzoumi

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Mohamad H. Makhzoumi

**Date:** 08/15/2025

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.

**Reporting Person:** Edward T. Mathers

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Edward T. Mathers

**Date:** 08/15/2025

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.

**Reporting Person:** Scott D. Sandell

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Scott D. Sandell

**Date:** 08/15/2025

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.

**Reporting Person:** Paul Walker

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Paul Walker

**Date:** 08/15/2025

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.

**Reporting Person:** Rick Yang

**Signature:** /s/ Zachary Bambach

**Name/Title:** Zachary Bambach as attorney-in-fact for Rick Yang

**Date:** 08/15/2025