Thinking Machines Lab Closes $2B Seed Round at $12B Valuation
Summary
Thinking Machines Lab, the AI startup founded by former OpenAI CTO Mira Murati, closed a $2 billion seed round at a $12 billion valuation — the largest seed round in Silicon Valley history. The round was led by Andreessen Horowitz with Nvidia as a co-investor. The company was founded in February 2025 by Murati and five colleagues who departed OpenAI, including John Schulman, Barret Zoph, Lilian Weng, Luke Tulloch, and Jason Metz. Thinking Machines launched the Tinker fine-tuning API in October 2025.
What Happened
Mira Murati resigned as OpenAI's Chief Technology Officer in September 2024, a departure that drew significant attention given her central role in the company's technical direction. In February 2025, Murati launched Thinking Machines Lab with five founding colleagues from OpenAI: John Schulman (who had also departed OpenAI in August 2024), Barret Zoph, Lilian Weng, Luke Tulloch, and Jason Metz. The collective departure of this group represented an extraordinary concentration of AI talent in a single new venture.
In July 2025, Thinking Machines closed a $2 billion seed round at a $12 billion valuation. Andreessen Horowitz led the investment, with Nvidia participating as a co-investor alongside other undisclosed participants. The $12 billion valuation on a seed round — before the company had shipped any significant product — set a new record for pre-revenue valuations at the seed stage.
In October 2025, Thinking Machines shipped Tinker, an API for fine-tuning foundation models. The product positioned the company as a tool for organizations seeking to adapt existing models rather than training from scratch — a distinct strategic bet compared to the foundation model training approach of OpenAI and Anthropic.
In January 2026, Barret Zoph returned to OpenAI, reducing the founding team. His departure from Thinking Machines was notable as the first significant change to the founding team composition.
Why It Matters
The Thinking Machines $2 billion seed round crystallized several dynamics of the 2025 AI investment environment. First, the talent premium: Murati and her co-founders commanded a $12 billion valuation with no product, no revenue, and a company five months old, entirely on the basis of the team's demonstrated capabilities at OpenAI. No prior startup in Silicon Valley history had achieved a comparable seed valuation.
Second, the Nvidia co-investment illustrates the compute-capital entanglement of the AI sector. Nvidia's participation in a seed round serves multiple purposes: financial return, early access to promising AI companies as customers, and influence over which labs receive GPU allocations in a constrained supply environment.
Third, Thinking Machines represents the talent dispersion pattern of a maturing AI frontier. As OpenAI grew from a research lab into a $300 billion company with 3,000+ employees and complex corporate pressures, some of its most senior technical talent elected to restart with smaller, more focused organizations. The capital environment of 2025 — where $12 billion seed valuations were achievable — made this calculus financially viable in a way it would not have been in earlier years.
The Tinker fine-tuning product, if successful, competes indirectly with the API businesses of OpenAI and Anthropic by enabling organizations to optimize models for specific applications rather than relying entirely on general-purpose frontier model APIs.