Sec Form 3 Filing - DiBiase Mary @ X4 Pharmaceuticals, Inc - 2021-09-08

FORM 3 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 DiBiase Mary 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) Chief Operating Officer (Last) (First) (Middle) C/O X4 PHARMACEUTICALS INC., 61 NORTH BEACON STREET 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/08/2021 (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 64,475 ( 1 ) 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) $ 6.84 ( 2 ) 07/11/2027 Common Stock 15,205 D Stock Option (right to buy) $ 7.08 ( 3 ) 04/10/2028 Common Stock 1,900 D Stock Option (right to buy) $ 10.44 ( 4 ) 08/21/2028 Common Stock 10,112 D Stock Option (right to buy) $ 14.75 ( 5 ) 06/16/2029 Common Stock 9,469 D Stock Option (right to buy) $ 10 ( 6 ) 02/09/2030 Common Stock 22,500 D Stock Option (right to buy) $ 8.69 ( 7 ) 06/09/2030 Common Stock 7,500 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other DiBiase Mary C/O X4 PHARMACEUTICALS INC. 61 NORTH BEACON STREET 4TH FLOOR BOSTON, MA02134 Chief Operating Officer Signatures /s/ Derek M. Meisner, attorney-in-fact 09/10/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes 58,293 shares underlying restricted stock units issued to the Reporting Person. Each restricted stock unit represents a contingent right to receive one share of common stock of the Issuer and has no expiration date. Of the total shares underlying outstanding restricted stock units, (a) 2,916 shares will vest on June 15, 2022; 2,917 shares will vest on June 23, 2022; 5,834 shares will vest on August 17, 2022; 2,916 shares will vest on June 15, 2023 and 2,917 shares will vest on June 23, 2023 (b) 3,156 shares will vest in two equal instalments on June 30, 2022 and June 30, 2023 and (c) 37,637 shares will vest in three equal instalments on February 11, 2022, February 11, 2023 and February 11, 2024, in each case subject to the Reporting Person providing continuous service to the Issuer on such dates. ( 2 )Fully vested as of July 12, 2021. ( 3 )Fully vested as of April 11, 2020. ( 4 )Twenty five percent (25%) of the shares underlying the option vested on August 22, 2019 and one thirty sixth (1/36th) of the shares underlying the award vest monthly thereafter subject to the reporting person providing continuous services to the Issuer on such dates. ( 5 )Twenty five percent (25%) of the shares underlying the option vested on June 17, 2020 and one thirty sixth (1/36th) of the shares underlying the award vest monthly thereafter subject to the reporting person providing continuous services to the Issuer on such dates. ( 6 )Twenty five percent (25%) of the shares underlying the option vested on February 10, 2021 and one thirty sixth (1/36th) of the shares underlying the award vest monthly thereafter subject to the reporting person providing continuous services to the Issuer on such dates. ( 7 )Twenty five percent (25%) of the shares underlying the option vested on June 10, 2021 and one thirty sixth (1/36th) of the shares underlying the award vest monthly thereafter subject to the reporting person providing continuous services to the Issuer on such dates.

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).

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