Chai Discovery, the OpenAI-backed biotech startup, closed a $130 million Series B financing round in December 2025 at a $1.3 billion valuation, bringing total funding to more than $225 million. The round was co-led by Oak HC/FT and General Catalyst, with participation from Thrive Capital, OpenAI, Dimension, Menlo Ventures, Lachy Groom, Yosemite, Neo, SV Angel, and new investors Emerson Collective and Glade Brook.
Chai-2: A Breakthrough in De Novo Antibody Design
The funding comes on the heels of the unveiling of Chai-2, a multimodal generative AI platform that achieved a landmark in fully de novo antibody design. In results published in mid-2025, Chai-2 demonstrated a 16% hit rate in zero-shot antibody design, representing a more than 100-fold improvement compared to previous computational methods. In a single round of experimental testing, at least one successful hit was found for 50% of targets tested, often with strong binding affinities and favorable drug-like profiles.
Chai-2 integrates an all-atom generative design module with a folding model that predicts antibody-antigen complex structures at double the accuracy of its predecessor, Chai-1. Experimentally determined structures of Chai-2-designed antibodies closely matched their computational predictions, demonstrating atomic-level accuracy in the design process.
Drug-Like Quality at AI Speed
Beyond binding, Chai-2 demonstrated that its designed antibodies possess genuinely drug-like properties:
- Over 86% of full-length monoclonal antibodies designed by Chai-2 showed strong developability profiles on par with approved therapeutic antibodies.
- The platform successfully designed functional antibodies mediating GPCR agonism and highly specific antibodies selectively binding tumor-specific neoepitopes.
- Researchers can move from in silico generation to lab validation in under two weeks, dramatically accelerating development timelines.
Company Background
Chai Discovery was founded in 2024 by Josh Meier, who previously worked in machine learning research at Meta (Facebook) and at OpenAI. The company builds frontier AI to predict and reprogram interactions between biochemical molecules, with a mission to transform biology from science into engineering. The $130 million Series B will fund further development of the Chai platform and expansion into therapeutic programs against challenging targets, including those historically considered undruggable.
Industry Significance
Chai Discovery's results represent a step change in the field of computational antibody design. Traditional methods for generating antibodies rely on immunizing animals or screening large combinatorial libraries, processes that can take months and often fail against difficult targets. Chai-2's zero-shot approach bypasses these limitations entirely, generating functional antibodies computationally before any experimental work begins. The involvement of OpenAI as an investor further underscores the convergence of frontier AI capabilities with biological applications, suggesting that advances in large-scale generative modeling are now mature enough to deliver tangible results in drug discovery.
