Chai Discovery Raises $400M Series C at $3.8B Valuation

Chai Discovery has closed a $400 million Series C financing round, valuing the San Francisco-based AI drug discovery company at $3.8 billion. The round brings the startup's total funding to more than $600 million across four rounds in less than two years.

Index Ventures, Kleiner Perkins, Sequoia Capital and Dimension led the latest investment, which follows commercial partnerships with Eli Lilly, Pfizer and Novartis announced earlier this year.

Why it matters

Chai's rapid ascent reflects a shift in how pharmaceutical companies approach AI-powered drug discovery. Rather than treating computational tools as experimental add-ons, major drugmakers are now integrating AI models directly into their discovery workflows. The company's ability to attract both top-tier venture backing and pharma partnerships signals that AI drug design is moving from research curiosity to production deployment.

From launch to commercial traction

Founded in 2024, Chai develops AI models that predict and reprogram molecular interactions. The company raised a $30 million seed round and released its first model, Chai-1, in its inaugural year. A $70 million Series A followed in August 2025 alongside the launch of Chai-2, then a $130 million Series B in December of that year.

The company has since released Chai-3 and signed deals with three of the world's largest pharmaceutical companies. According to CEO and co-founder Joshua Meier, these partnerships demonstrate that AI drug discovery has progressed "from promise to deployment."

"Companies are using Chai's models to design better molecules, move faster against difficult targets and take on challenges that traditional discovery methods have struggled to solve," Meier said in a statement.

Technical performance claims

Chai has published preprint papers detailing the performance of its models. One study reported that Chai-2 achieved a 16% hit rate in fully de novo antibody design when given a defined epitope on a target. The company characterized this result as 100-fold better than earlier computational methods and sufficient to bypass high-throughput screening in some cases.

A follow-up paper indicated that antibodies generated by the model possess drug-like properties and can engage difficult targets. The startup's investors cited this real-world validation by leading pharmaceutical companies as a key factor in their decision to participate in the Series C.

Next steps

Chai has disclosed limited information about how it plans to deploy the new capital, stating only that the funds will "further accelerate progress." The company has not announced specific expansion plans or additional partnerships.

The details were first reported by Fierce Biotech.