Sanofi and Regeneron expanded their long-running immunology partnership to develop additional long-acting antibody drugs targeting the same pathways as Dupixent. The agreement includes a $1 billion upfront payment and up to $8 billion in development, regulatory, and commercial milestones. Regeneron is set to lead research and development, while Sanofi will handle global commercialization, with cost sharing and profit splitting outlined in the deal. The companies described the expanded portfolio as designed to reach pivotal testing by 2029, ahead of Dupixent patent expiration in 2031. The move reflects large-scale re-investment into “next-wave” IL-4/IL-13 biology as blockbuster patent cliffs approach—using modular platform extensions rather than entirely new targets.