Biogen struck a deal to buy RayThera for up to $1 billion, aiming to add a portfolio of early immunology assets to its pipeline. The acquisition is structured with an undisclosed upfront payment and backloaded milestone payments tied to clinical and regulatory progress. RayThera, a secretive startup founded in 2023, has publicly referenced anti-inflammatory drug candidates but provided limited detail on specific targets. The deal reflects Biogen’s effort to widen beyond its neurology focus, especially as the company integrates other recent acquisitions, including the $5.6 billion purchase of Apellis. Industry observers noted RayThera’s prior funding—an April 2025 Series A led by Foresite Capital and OrbiMed Advisors—positioned the company to advance programs quickly despite limited public disclosure. The purchase also highlights a continued appetite for immunology exposure where target biology and safety profiles remain central to differentiation. For immunology-focused investors and partners, the backloaded structure underscores how Biogen is treating these assets as optionality—paying most as clinical milestones are reached.