Amgen terminated its collaboration with Kyowa Kirin on an anti‑OX40 autoimmune candidate, returning rights to Kyowa Kirin despite Amgen having run extensive pivotal programs and achieved Phase 3 datasets. Amgen’s exit transfers responsibility — and future regulatory risk — back to Kyowa Kirin ahead of planned filings. Industry reporting indicates the split was abrupt and follows a five‑year partnership that included up‑front payments and shared development work. Kyowa Kirin now inherits costs and strategic decisions for the asset, including whether to pursue an FDA submission or seek new partners. The break underscores how large biotechs will walk away from collaborations when pipeline priorities shift or when late‑stage readouts and commercial prospects alter internal ROI calculations. The move also highlights the financial and programmatic consequences small and mid‑cap biotech partners face when major collaborators withdraw before regulatory milestones are reached.