Sanofi will pay Regeneron $1 billion upfront to expand their antibody collaboration as the Dupixent patent cliff nears. The agreement extends Sanofi’s immunology alliance, aiming to add new programs and keep pipeline momentum as competitive pressure increases. The structure echoes earlier partnership mechanics between the two companies: large upfront payments tied to expanded R&D scope, plus milestone- and royalty-style economics. For Regeneron, the deal provides capital to support additional antibody development work within the broader collaboration platform. The announced expansion reinforces the continued reliance on immunology alliances to extend late-stage franchise value and diversify antibody exposure beyond any single asset lifecycle.