License, and Funding Agreements	6 Months Ended
Jun. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License, and Funding Agreements	LICENSE AND FUNDING ARRANGEMENTS Research and Development Incentive Program The Company participated in a research and development incentive program provided by the Austrian government whereby the Company was entitled to reimbursement by the Austrian government for a percentage of qualifying research and development expenses and capital expenditures incurred by the Company’s subsidiary in Austria. As of June 30, 2025, the amount due under the program was $0.7 million, which amount is included in research and development incentive receivable in the condensed consolidated balance sheet. During the three and six months ended June 30, 2025 no amounts were recorded for this program as the Company is in the process of closing the Vienna site. During the three and six months ended June 30, 2024, the Company recorded $0.1 million and $0.3 million, respectively, of income related to the program within the condensed consolidated statement of operations as other income. Genzyme Agreement In July 2014, the Company entered into a license agreement with Genzyme (the “Genzyme Agreement”) pursuant to which the Company was granted an exclusive license to certain patents and intellectual property owned or controlled by Genzyme related to the CXCR4 receptor to develop and commercialize products containing licensed compounds (including but not limited to mavorixafor) for all therapeutic, prophylactic and diagnostic uses, with the exception of autologous and allogenic human stem cell therapy. Under the terms of the Genzyme Agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize licensed products for use in the field in the United States and at least one other major market country. The Company has the right to grant sublicenses of the licensed rights that cover mavorixafor to third parties. Under the Genzyme Agreement, the Company is obligated to make milestone payments contingent upon the achievement of certain regulatory and sales milestones with respect to licensed products. During the six months ended June 30, 2025, a $3.0 million regulatory milestone, which had been previously accrued, was paid after receipt of the European Medicines Agency’s (“EMA”) validation of the Company’s Marketing Authorisation Application (“MAA”) for processing. The payment was recorded as a definite-lived intangible asset as discussed in Note 8. In addition, for the three and six months ended June 30, 2025, the Company incurred $0.1 million and $4.5 million, respectively, of royalty payments under the Genzyme Agreement as a result of sublicense payments received and sales of licensed product. Such royalty payments were recorded as cost of revenue. As of June 30, 2025, the Company is obligated to make future milestone payments in the aggregate amount of up to $10.0 million, including $5.0 million upon the notification by the EMA of regulatory approval of the Company’s MAA for WHIM and one-time sales milestone payments of $0.5 million, $1.5 million and $3.0 million on cumulative net sales of $50.0 million, $150.0 million and $300.0 million, respectively. As of June 30, 2025, the Company accrued $0.5 million of sales-based milestones as a component of the definite-lived intangible asset, as management has concluded that the achievement of this milestones is probable. The Company is also obligated to pay Genzyme tiered royalties based on net sales of licensed products that the Company commercializes under the agreement. Upon the first sale of the Company’s drug candidate in the U.S., the Company incurred a royalty on annual net sales at a rate of 6%, and will incur royalties on annual net sales at a rate of 6% up to $150.0 million, 10% on the portion of annual net sales between $150.0 million and $300.0 million, and 12% thereafter on annual sale over $300.0 million. The Company also incurs a 15% royalty on certain sublicense payments received from sub-licensees. The obligation to pay royalties for each licensed product expires on a country-by-country basis on the latest of (i) the expiration of licensed patent rights that cover that licensed product in that country, (ii) the expiration of regulatory exclusivity in that country and (iii) ten years after the first commercial sale of such licensed product in that country. Royalty rates are subject to reduction under the agreement in specified circumstances, including in any country if the Company is required to obtain a license from any third party to the extent the Company’s patent rights might infringe the third party’s patent rights, if a licensed product is not covered by a valid claim in that country or if sales of generic products reach certain thresholds in that country. If the Company enters into a sublicense under the Genzyme Agreement, the Company will be obligated to pay Genzyme a percentage of certain upfront fees, maintenance fees, milestone payments and royalty payments paid to the Company by the sublicensee. Under the Genzyme Agreement, the Company will itself manufacture and supply, or enter into manufacturing or supply agreements with Genzyme or third parties to manufacture and supply, clinical and commercial supplies of licensed compounds and each licensed product. The Company is also responsible for all costs related to the filing, prosecution and maintenance of the licensed patent rights. The Genzyme Agreement will remain in effect until the expiration of the royalty term in all countries for all licensed products. The Genzyme Agreement may be terminated by either party with at least 90 days’ notice in the event of material breach by the other party that remains uncured for 90 days, by either party for insolvency or bankruptcy of the other party, immediately by Genzyme if the Company challenges the licensed patents, or immediately by the Company if a material safety issue arises. Norgine Agreement On January 13, 2025, the Company entered into a License and Supply Agreement (the “Norgine Agreement”) with Norgine Pharma UK Limited (“Norgine”), pursuant to which Norgine was granted an exclusive license to seek regulatory approval and distribute, market and sell the Company’s product mavorixafor (marketed by the Company as XOLREMDI in the United States) within the Field (as defined in the Norgine Agreement), in the European Economic Area, Switzerland, the United Kingdom, Australia and New Zealand (collectively, the “Territory”), following regulatory approval in the Territory. Additionally, Norgine was granted a co-exclusive license to manufacture mavorixafor for the Territory. The Company retains all rights to mavorixafor outside the Territory and specific reserved rights within the Territory. Norgine may grant sublicenses to its affiliates and certain third parties subject to the terms of the Norgine Agreement, except that it may not sublicense the commercial rights granted under the Norgine Agreement for certain countries without X4’s explicit consent. Pursuant to the terms of the Norgine Agreement, the Company received a one-time, non-refundable, upfront payment of €28.5 million and a regulatory milestone payment of €0.5 million. The Company could receive up to approximately €20.6 million, €20.0 million and €185.0 million upon the achievement of certain regulatory, commercial, and sales milestones, respectively, or €225.6 million in aggregate. The Norgine Agreement also includes escalating double-digit royalties of up to mid-twenties on any future net sales in the Territory. The tiered royalty payments are subject to royalty stacking, and to a material reduction on a country-by-country basis if a generic version of mavorixafor becomes available in the applicable country. The Company and Norgine will collaborate closely on regulatory filings, with the Company continuing to be responsible for the ongoing global, pivotal Phase 3 4WARD clinical trial evaluating mavorixafor in chronic neutropenia and certain components of pediatric studies for WHIM. Norgine will be responsible for all market access and commercialization activities. The Company also agreed to manufacture and supply mavorixafor to Norgine. Norgine shall be required to pay a supply price to the Company for the licensed product derived from the Company’s manufacturing costs plus margin in the low teens. Subject to customary rights of each party to earlier terminate the Norgine Agreement, the term of the Norgine Agreement continues, on a country-by-country basis, until the later of: (i) the tenth (10th) anniversary of the first commercial sale of mavorixafor, (ii) expiration of regulatory market exclusivity of mavorixafor or (iii) expiration of the last-to-expire licensed patent in such country. The term of the Norgine Agreement shall be automatically renewed for additional three-year terms unless either party provides the other party written notice of its intent not to renew the Agreement at least one year prior to the applicable termination date of the Agreement. In the event of automatic renewal, the royalty payment rate drops to a single digit royalty.

The Company participated in a research and development incentive program provided by the Austrian government whereby the Company was entitled to reimbursement by the Austrian government for a percentage of qualifying research and development expenses and capital expenditures incurred by the Company’s subsidiary in Austria. As of June 30, 2025, the amount due under the program was $0.7 million, which amount is included in research and development incentive receivable in the condensed consolidated balance sheet. During the three and six months ended June 30, 2025 no amounts were recorded for this program as the Company is in the process of closing the Vienna site. During the three and six months ended June 30, 2024, the Company recorded $0.1 million and $0.3 million, respectively, of income related to the program within the condensed consolidated statement of operations as other income.

In July 2014, the Company entered into a license agreement with Genzyme (the “Genzyme Agreement”) pursuant to which the Company was granted an exclusive license to certain patents and intellectual property owned or controlled by Genzyme related to the CXCR4 receptor to develop and commercialize products containing licensed compounds (including but not limited to mavorixafor) for all therapeutic, prophylactic and diagnostic uses, with the exception of autologous and allogenic human stem cell therapy. Under the terms of the Genzyme Agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize licensed products for use in the field in the United States and at least one other major market country. The Company has the right to grant sublicenses of the licensed rights that cover mavorixafor to third parties.

Under the Genzyme Agreement, the Company is obligated to make milestone payments contingent upon the achievement of certain regulatory and sales milestones with respect to licensed products. During the six months ended June 30, 2025, a $3.0 million regulatory milestone, which had been previously accrued, was paid after receipt of the European Medicines Agency’s (“EMA”) validation of the Company’s Marketing Authorisation Application (“MAA”) for processing. The payment was recorded as a definite-lived intangible asset as discussed in Note 8. In addition, for the three and six months ended June 30, 2025, the Company incurred $0.1 million and $4.5 million, respectively, of royalty payments under the Genzyme Agreement as a result of sublicense payments received and sales of licensed product. Such royalty payments were recorded as cost of revenue.

As of June 30, 2025, the Company is obligated to make future milestone payments in the aggregate amount of up to $10.0 million, including $5.0 million upon the notification by the EMA of regulatory approval of the Company’s MAA for WHIM and one-time sales milestone payments of $0.5 million, $1.5 million and $3.0 million on cumulative net sales of $50.0 million, $150.0 million and $300.0 million, respectively. As of June 30, 2025, the Company accrued $0.5 million of sales-based milestones as a component of the definite-lived intangible asset, as management has concluded that the achievement of this milestones is probable.

The Company is also obligated to pay Genzyme tiered royalties based on net sales of licensed products that the Company commercializes under the agreement. Upon the first sale of the Company’s drug candidate in the U.S., the Company incurred a royalty on annual net sales at a rate of 6%, and will incur royalties on annual net sales at a rate of 6% up to $150.0 million, 10% on the portion of annual net sales between $150.0 million and $300.0 million, and 12% thereafter on annual sale over $300.0 million. The Company also incurs a 15% royalty on certain sublicense payments received from sub-licensees.

The obligation to pay royalties for each licensed product expires on a country-by-country basis on the latest of (i) the expiration of licensed patent rights that cover that licensed product in that country, (ii) the expiration of regulatory exclusivity in that country and (iii) ten years after the first commercial sale of such licensed product in that country. Royalty rates are subject to reduction under the agreement in specified circumstances, including in any country if the Company is required to obtain a license from any third party to the extent the Company’s patent rights might infringe the third party’s patent rights, if a licensed

product is not covered by a valid claim in that country or if sales of generic products reach certain thresholds in that country. If the Company enters into a sublicense under the Genzyme Agreement, the Company will be obligated to pay Genzyme a percentage of certain upfront fees, maintenance fees, milestone payments and royalty payments paid to the Company by the sublicensee. Under the Genzyme Agreement, the Company will itself manufacture and supply, or enter into manufacturing or supply agreements with Genzyme or third parties to manufacture and supply, clinical and commercial supplies of licensed compounds and each licensed product. The Company is also responsible for all costs related to the filing, prosecution and maintenance of the licensed patent rights.

The Genzyme Agreement will remain in effect until the expiration of the royalty term in all countries for all licensed products. The Genzyme Agreement may be terminated by either party with at least 90 days’ notice in the event of material breach by the other party that remains uncured for 90 days, by either party for insolvency or bankruptcy of the other party, immediately by Genzyme if the Company challenges the licensed patents, or immediately by the Company if a material safety issue arises.

On January 13, 2025, the Company entered into a License and Supply Agreement (the “Norgine Agreement”) with Norgine Pharma UK Limited (“Norgine”), pursuant to which Norgine was granted an exclusive license to seek regulatory approval and distribute, market and sell the Company’s product mavorixafor (marketed by the Company as XOLREMDI in the United States) within the Field (as defined in the Norgine Agreement), in the European Economic Area, Switzerland, the United Kingdom, Australia and New Zealand (collectively, the “Territory”), following regulatory approval in the Territory. Additionally, Norgine was granted a co-exclusive license to manufacture mavorixafor for the Territory. The Company retains all rights to mavorixafor outside the Territory and specific reserved rights within the Territory. Norgine may grant sublicenses to its affiliates and certain third parties subject to the terms of the Norgine Agreement, except that it may not sublicense the commercial rights granted under the Norgine Agreement for certain countries without X4’s explicit consent.

Pursuant to the terms of the Norgine Agreement, the Company received a one-time, non-refundable, upfront payment of €28.5 million and a regulatory milestone payment of €0.5 million. The Company could receive up to approximately €20.6 million, €20.0 million and €185.0 million upon the achievement of certain regulatory, commercial, and sales milestones, respectively, or €225.6 million in aggregate. The Norgine Agreement also includes escalating double-digit royalties of up to mid-twenties on any future net sales in the Territory. The tiered royalty payments are subject to royalty stacking, and to a material reduction on a country-by-country basis if a generic version of mavorixafor becomes available in the applicable country. The Company and Norgine will collaborate closely on regulatory filings, with the Company continuing to be responsible for the ongoing global, pivotal Phase 3 4WARD clinical trial evaluating mavorixafor in chronic neutropenia and certain components of pediatric studies for WHIM. Norgine will be responsible for all market access and commercialization activities. The Company also agreed to manufacture and supply mavorixafor to Norgine. Norgine shall be required to pay a supply price to the Company for the licensed product derived from the Company’s manufacturing costs plus margin in the low teens.

Subject to customary rights of each party to earlier terminate the Norgine Agreement, the term of the Norgine Agreement continues, on a country-by-country basis, until the later of: (i) the tenth (10th) anniversary of the first commercial sale of mavorixafor, (ii) expiration of regulatory market exclusivity of mavorixafor or (iii) expiration of the last-to-expire licensed patent in such country. The term of the Norgine Agreement shall be automatically renewed for additional three-year terms unless either party provides the other party written notice of its intent not to renew the Agreement at least one year prior to the applicable termination date of the Agreement. In the event of automatic renewal, the royalty payment rate drops to a single digit royalty.