CSL Behring disclosed a temporary global stockout of its hemophilia B gene therapy, warning that supply constraints could delay treatment for some patients. The company communicated the shortage in a letter to the patient community and said it is taking steps to restore manufacturing and equitable allocation. The announcement highlights how limited manufacturing capacity, complex supply chains and single‑source production can interrupt access to one‑time advanced therapies. Clinicians and treatment centers face difficult triage decisions while companies and regulators weigh mitigation options including scaled production, import waivers and bridging therapies. Longer term, the incident is likely to accelerate industry investment in redundant manufacturing capacity, better inventory planning and regulatory pathways for contingency supply to protect continuity of care for patients reliant on gene therapies.