XFOR X4 Pharmaceuticals Inc

X4 Pharmaceuticals, Inc.

61 North Beacon Street, 4th Floor

Boston, Massachusetts 02134

OrbiMed Advisors KKC

OrbiMed Capital GP IV LLC

601 Lexington Avenue, 54th Floor

New York, NY 10022

Please refer to Item 4 on each cover sheet for each filing person.

Common Stock, par value $0.001 per share

98420X103

Item 3.

OrbiMed Capital GP IV LLC (“GP IV”) is the general partner of OrbiMed Private Investments IV, LP (“OPI IV”). OrbiMed Advisors LLC (“Advisors”) is an investment advisor in accordance with ss.240.13d-1(b)(1)(ii)(E) and is the managing member of GP IV.

 Item 4. Ownership:

Information with respect the Reporting Persons’ ownership as of December 31, 2022 is incorporated by reference to items (5) – (9) and (11) of the cover page for the Reporting Person.

Item 5. Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date hereof the Reporting Person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following ☐.

Item 6. Ownership of More Than Five Percent on Behalf of Another Person.

Reporting Persons are holding 8.2% of the shares in the aggregate on behalf of other persons who have the right to receive or the power to direct the receipt of dividends from, or proceeds from the sale of, such securities. No one such other person’s interest in the securities whose ownership is reported here relates to more than five percent of the class. Advisors exercises investment and voting power over the shares through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Common Stock reported herein.

Item 7. Identification and Classification of the Subsidiary which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

Not Applicable.

Item 8. Identification and Classification of Members of the Group.

Not Applicable.

Item 9. Notice of Dissolution of Group.

Not Applicable.

Item 10. Certification.

By signing below, I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and 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.

SIGNATURES

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.

Dated: February 14, 2023