Chai Discovery raises $400M Series C at $3.8B

Index Ventures led the round, with Kleiner Perkins, Sequoia Capital and Dimension as co-leads. Bain Capital Ventures, Battery Ventures and Baillie Gifford joined as new investors, while Thrive Capital, OpenAI and Menlo Ventures kept their positions. The prior round was a $130 million Series B in December 2025 at a $1.3 billion valuation, and this is the third financing in less than a year. Total funding now sits near $630 million. Commercial traction underpins the price. This year Chai signed deals with Lilly, Pfizer and Novartis, and it released Chai-3. Forbes reported in June that the company was in talks at a $3.4 billion valuation, so the final number came in higher than first reported. Caveats remain: the valuation sits on zero clinically validated compounds, which makes it a bet on the tooling rather than on outcomes. For AI founders, the round shows investors will pay up for model companies that have paying enterprise customers in a regulated industry, not just benchmark results. One analysis argues the scarce asset is proprietary experimental data and deployment history, not the foundation model itself, as shown by Pfizer licensing a private model trained on its own data. Startups selling into pharma or similar sectors may find that customer-specific data arrangements matter as much as model quality.