- Weng said July 28 would be her final day at Thinking Machines after sustained stress and workload exceeded what her health could support. [1] - OpenAI confirmed that Weng will lead a top-level team supporting research across the company, including work on recursive self-improvement, but did not provide a start date. [2] - Thinking Machines has not disclosed how the departure affects Weng’s founder equity or responsibilities; reported governance terms give CEO Mira Murati control of the board.
[3] OpenAI says Lilian Weng will return to the company after the AI researcher and co-founder left Thinking Machines Lab, citing the physical toll of sustained startup work. Her final day at Thinking Machines was July 28.[1]
An OpenAI spokesperson said Weng will lead a top-level team intended to accelerate internal research and support work across research groups, including projects involving recursive self-improvement. OpenAI did not disclose her formal title or start date, and Thinking Machines has not publicly confirmed when she begins the new position.[2]
A narrower role after co-founder pressures #
Weng wrote that consistent stress and workload had pushed her beyond what her health could sustain. She said she remained interested in AI research but needed a more predictable environment and a position with clearer boundaries than the role of a co-founder.[1]
Thinking Machines CEO Mira Murati publicly backed the decision, writing that she was glad Weng was putting her health first. The company has not announced a replacement or explained how her research and leadership duties will be reassigned.[4]
Weng previously spent nearly seven years at OpenAI, where she worked on robotics and applied research, created the Safety Systems team and became vice president of research and safety before leaving in November 2024. [5] Her new assignment is broader than her former safety post, according to OpenAI’s description, and places her in a research area focused on systems that can contribute to improving AI development itself.
[2]The companies also left the financial and governance consequences unclear. Neither disclosed whether Weng retains vested founder shares, forfeits unvested equity or held a board seat. Her exit does not necessarily change control: investment documents previously reported by The Information gave Murati a board vote equal to all other directors’ votes combined, plus one. [3] Thinking Machines raised $2 billion at a $12 billion valuation in 2025, making any undisclosed founder stake potentially significant.
[6]## Companies mentioned
Further sources #
[1] Lilian Weng, departure statement on X, July 27, 2026; QbitAI account of the ful… ↗ [2] TechCrunch, “Thinking Machines co-founder Lilian Weng left the company citing h… ↗
[[3] The Information, “Thinking Machines Lab CEO Has Unusual Control in Andreessen-L… ↗](https://www.theinformation.com/articles/thinking-machines-lab-ceo-unusual-control-andreessen-led-deal/)
[[4] Mira Murati, response to Weng’s departure statement on X, July 27, 2026. ↗](https://x.com/miramurati/status/2081835376449363986)
[[5] TechCrunch, “OpenAI loses another lead safety researcher, Lilian Weng,” Novembe… ↗](https://techcrunch.com/2024/11/08/openai-loses-another-lead-safety-researcher-lilian-weng/)
[[6] WIRED, “Thinking Machines Lab Raises a Record $2 Billion, Announces Cofounders,… ↗](https://www.wired.com/story/thinking-machines-lab-mira-murati-funding/)
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