X0609 4 2026-06-30 0 0001501697 X4 Pharmaceuticals, Inc XFOR 0001276750 KIRSKE DAVID false C/O X4 PHARMACEUTICALS INC. 61 N BEACON STREET, 4TH FLOOR BOSTON MA 02134 0 1 0 0 Chief Financial Officer 0 Common Stock 2026-06-30 4 S 0 8543 4.2641 D 167750 D Sale of shares to cover personal income tax obligation upon settlement of restricted stock unit award. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $4.21 to $4.31, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. Of the shares of common stock reported, 96,627 shares represent restricted stock units. /s/ Mitch Buckley, attorney-in-fact 2026-07-01