SCHEDULE 13G 0002068530 XXXXXXXX LIVE Common Stock, par value $0.001 per share 10/03/2025 0001501697 X4 Pharmaceuticals, Inc. 98420X202 61 North Beacon Street, 4th Floor, Boston MA 02134 Rule 13d-1(b) Rule 13d-1(c) Coastlands Capital LP b DE 0.00 2491638.00 0.00 2491638.00 2491638.00 N 9.99 IA PN 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%. Coastlands Capital Partners LP b DE 0.00 2491638.00 0.00 2491638.00 2491638.00 N 9.99 PN 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%. Coastlands Capital GP LLC b DE 0.00 2491638.00 0.00 2491638.00 2491638.00 N 9.99 OO 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%. Coastlands Capital LLC b DE 0.00 2491638.00 0.00 2491638.00 2491638.00 N 9.99 HC OO 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%. Matthew D. Perry b X1 0.00 2491638.00 0.00 2491638.00 2491638.00 N 9.99 HC IN 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%. X4 Pharmaceuticals, Inc. 61 North Beacon Street, 4th Floor Boston, MA, 02134 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. 601 California Street, Suite 1210, San Francisco, CA 94108 See Item 4 of the cover sheet for each reporting person. N IA HC Coastlands: 2,491,638 Partnership: 2,491,638 General Partner: 2,491,638 Coastlands GP: 2,491,638 Matthew D. Perry: 2,491,638 Coastlands: 9.99% Partnership: 9.99% General Partner: 9.99% Coastlands GP: 9.99% Matthew D. Perry: 9.99% Coastlands: 0 Partnership: 0 General Partner: 0 Coastlands GP: 0 Matthew D. Perry: 0 Coastlands: 2,491,638 Partnership: 2,491,638 General Partner: 2,491,638 Coastlands GP: 2,491,638 Matthew D. Perry: 2,491,638 Coastlands: 0 Partnership: 0 General Partner: 0 Coastlands GP: 0 Matthew D. Perry: 0 Coastlands: 2,491,638 Partnership: 2,491,638 General Partner: 2,491,638 Coastlands GP: 2,491,638 Matthew D. Perry: 2,491,638 Y N 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. Y Y Y N 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. Exhibit 99.1 - Agreement Regarding Joint Filing of Statement on Schedule 13D or 13G (incorporated by reference to Exhibit 99.1 to the Schedule 13D filed on August 18, 2025) Coastlands Capital LP /s/ Mark Shamia 10/03/2025 Coastlands Capital Partners LP /s/ Mark Shamia 10/03/2025 Coastlands Capital GP LLC /s/ Mark Shamia 10/03/2025 Coastlands Capital LLC /s/ Mark Shamia 10/03/2025 Matthew D. Perry /s/ Matthew D. Perry 10/03/2025