X4 Pharmaceuticals, Inc

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

For the annual period ended December 31, 2025

or

For the transition period from __________ to __________

Commission File Number:001-38295

(Exact name of registrant as specified in its charter)

(857)529-8300

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None.

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes☐ No ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes☐ No ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C.7262(b)) by the registered public accounting firm that prepared or issued its audit report. Yes ☐ No ☒

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes☐ No ☒

On June 30, 2025, the aggregate market value of the registrant’s voting common stock held by non-affiliates of the registrant was approximately $14.9 million based upon the closing sale price on the Nasdaq Capital Market reported on June 30, 2025. In determining the market value of non-affiliate common stock, shares of the registrant’s common stock beneficially owned by officers, directors and affiliates have been excluded. This determination of affiliate status is not necessarily a conclusive determination for other purposes.

Independent Registered Public Accounting Firm PricewaterhouseCoopers LLP Boston, Massachusetts, US Firm ID 238

As of March 12, 2026, the registrant had 90,919,696 shares of common stock, $0.001 par value per share, outstanding.

Documents Incorporated by Reference

Portions of the registrant’s definitive proxy statement, (the “2026 Proxy Statement”) for its 2026 Annual Meeting of Stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2025, are incorporated by reference into Part III of this Annual Report on Form 10-K.

EXPLANATORY NOTE

On April 28, 2025, X4 Pharmaceuticals, Inc. (the “Company”), effected a 1-for-30 reverse stock split of its common stock (the “Reverse Stock Split”). Unless otherwise noted, all references to common stock share and per share amounts in this Annual Report on Form 10-K have been retroactively adjusted to reflect the Reverse Stock Split.

See Note 14, “Common Stock and Preferred Stock” of the consolidated financial statements for a description of the Reverse Stock Split.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). All statements, other than statements of historical facts, contained in this Annual Report on Form 10-K, including statements regarding our plans, objectives, goals, strategies, future events, future operations, future financial position, future revenues or performance, projected costs, prospects, expectations, plans or intentions relating to clinical development, product candidates, the regulatory approval process, products and markets, and business trends and other information referred to in the sections titled “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” are forward-looking statements. In some cases, these statements may be identified by such forward-looking terminology as “may,” “should,” “expects,” “intends,” “plans,” “anticipates,” “believes,” “estimates,” “predicts,” “potential,” “continue” or the negative of these terms or other comparable terminology. Our forward-looking statements are based on a series of expectations, assumptions, estimates and projections about our company, are not guarantees of future results or performance and involve substantial risks and uncertainty. We may not actually achieve the plans, intentions, or expectations disclosed in these forward-looking statements and actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements. These forward-looking statements are subject to a number of known and unknown risks, uncertainties and assumptions, including risks described in the section titled “Risk Factors” and elsewhere in this report, regarding, among other things:

•our ability to raise additional capital or achieve sufficient revenue to properly fund our business and operating plan as well as our ability to continue as a going concern;

•our expectations and goals for commercialization of XOLREMDI®(mavorixafor), which has been approved for use as an oral, once-daily therapy to increase the number of circulating mature neutrophils and lymphocytes in patients 12 years of age and older with WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome in the U.S., and that XOLREMDI, our one product approved for commercial sale, upon which we depend almost entirely to produce revenue, faces an unknown market size and growth potential, and we have not generated significant revenue from product sales to date, and we may never achieve profitability;

•the initiation, timing, progress and results of our current and future preclinical studies and clinical trials and related preparatory work and the period during which the results of the trials will become available, as well as our research and development programs;

•the potential benefits, including clinical utility, that may be derived from XOLREMDI or any of our product candidates;

•the timing of and our ability to obtain and maintain regulatory approval of our existing product XOLREMDI or any product candidates that we may develop in the future, and any related restrictions, limitations, or warnings in the label of any approved product candidates;

•our plans to research, develop, manufacture and commercialize XOLREMDI or our product candidates;

•the timing of our regulatory filings for our product candidates, along with regulatory developments in the United States and other foreign countries;

•the size and growth potential of the markets for XOLREMDI and our product candidates, if approved, and the rate and degree of market acceptance of XOLREMDI and our product candidates, including reimbursement that may be received from payors;

•the benefits of U.S. Food and Drug Administration (“FDA”) and European Commission (“EC”) designations, including, without limitation, Fast Track, Orphan Drug and Breakthrough Therapy;

•our commercialization, marketing and manufacturing capabilities and strategy;

•our ability to attract and retain qualified employees and key personnel;

•our competitive position and the development of and projections relating to our competitors or our industry;

•our expectations regarding our ability to obtain and maintain intellectual property protection;

•the success of competing therapies that are or may become available;

•our estimates and expectations regarding future operations, financial position, revenues, costs, expenses, uses of cash, capital requirements or our need for additional financing;

•our plans to in-license, acquire, develop and commercialize additional product candidates;

•the impact of laws and regulations;

•our plans to identify additional product candidates with significant commercial potential that are consistent with our commercial objectives;

•our strategies, prospects, plans, expectations or objectives; and

•other risks and uncertainties, including those listed under the section titled “Risk Factors” in this Annual Report.

You should refer to the section titled “Risk Factors” in this Annual Report for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. As a result of these factors, we cannot assure you that the forward-looking statements in this Annual Report will prove to be accurate. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law. You should, therefore, not rely on these forward-looking statements as representing our views as of any date subsequent to the date of this Annual Report.