Sec Form 4 Filing - Volpone John @ X4 Pharmaceuticals, Inc - 2025-08-12

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Volpone John 2. Issuer Name and Ticker or Trading Symbol X4 Pharmaceuticals, Inc [ XFOR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) President (Last) (First) (Middle) C/O X4 PHARMACEUTICALS INC., 61 NORTH BEACON STREET 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 08/12/2025 (Street) BOSTON, MA02134 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 08/14/2025 A 289,881 ( 1 ) A $ 0 289,881 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (right to buy) $ 1.42 08/12/2025 A 1,609,873 ( 2 ) 08/12/2035 Common Stock 1,609,873 $ 0 1,609,873 D Stock Option (right to buy) $ 3.14 08/14/2025 A 529,201 ( 2 ) 08/14/2035 Common Stock 529,201 $ 0 529,201 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Volpone John C/O X4 PHARMACEUTICALS INC. 61 NORTH BEACON STREET 4TH FLOOR BOSTON, MA02134 President Signatures /s/ Brian Bowersox, Attorney-In-Fact 08/14/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents restricted stock units (RSUs) granted to the Reporting Person. One third of the RSUs shall vest on each of August 12, 2026, August 12, 2027 and August 12, 2028, subject to the Reporting Person continuing to provide services through each such date and contingent upon approval of the grant at the Issuer's 2026 Annual Meeting of Stockholders. ( 2 )One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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