Chai Discovery has continued its whirlwind emergence, closing its third financing round in less than a year to bring its total funding haul above $600 million. The latest round values the startup at $3.8 billion.
San Francisco-based Chai develops AI models that predict and reprogramme the interactions between molecules. Founded in 2024, the startup raised a $30 million seed round and launched its first AI model, Chai-1, in its first year. Chai then raised a $70 million series A round and unveiled Chai-2 in August 2025, before closing a $130 million series B round in December.
This year, Chai has struck deals with Lilly, Pfizer and Novartis and unveiled Chai-3. The deals helped Chai raise its biggest round yet, with partners at Index Ventures, Kleiner Perkins and Sequoia Capital all citing real-world use of the startup’s AI by leading drugmakers to explain their participation in the series C.
AI drug discovery has moved “from promise to deployment,” Joshua Meier, co-founder and CEO of Chai, said in a statement. 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,” the CEO said.
Chai backed up its claims in preprint papers. One study found that, given a defined epitope on a target, Chai-2 achieved (PDF) a 16% hit rate in fully de novo antibody design. Chai argued the result was 100-fold better than earlier computational methods and high enough to reliably skip high-throughput screening. A subsequent paper showed (PDF) the antibodies have drug-like properties and can hit hard targets.
The startup has said little publicly about its next steps, limiting discussion of its plans for the series C to the aspiration to “further accelerate progress.” Index Ventures led the round alongside Kleiner Perkins, Sequoia Capital and Dimension.