Lilian Weng flips from Thinking Machines to OpenAI after saying the startup’s pace hurt her health

• Thinking Machines Lab cofounder Lilian Weng returns to OpenAI, leading an AI research team.
• Weng said she left Thinking Machines Lab for health reasons, writing that the gig was grueling.
• At OpenAI, she’ll support the high-stakes push to build AI models that can improve their successors.

Lilian Weng, a cofounder of the AI startup Thinking Machines Lab who stepped down this week, is rejoining OpenAI.

The researcher will lead a team focused on accelerating internal research at the ChatGPT maker, as part of OpenAI’s bid to develop AI that can improve itself, a company spokesperson told Business Insider.

Weng had shared on Monday that she would be leaving Thinking Machines after a grueling stretch at the startup, writing, “I don’t feel I’m able to continue at the pace a startup requires.”

“It has been an extremely hard decision, as I hate myself to let down people at Thinky but at the same time I’m constantly worried about my health,” she added, referring to the startup’s nickname.

Weng wrote that she still enjoys working in the field and reading papers about frontier AI progress, saying that a “scoped role in a more predictable place, and not as a cofounder” would suit her better.

That role will now be at OpenAI, the company where Weng worked from 2018 until late 2024, after stints at Facebook, Dropbox, and Affirm. During her first tenure at OpenAI, she helped build the Applied AI Research team and later led its Safety Systems work.

Weng and Thinking Machines Lab didn’t immediately respond to requests for comment.

Previously, Weng helped develop OpenAI’s GPT-4 model, working on pretraining data, model safety, evaluations, and deployment.

Upon her return, Weng will lead a team supporting OpenAI’s high-stakes effort to achieve “recursive self-improvement,” in which AI models can train and improve their successors.

The OpenAI spokesperson praised Weng’s combination of research experience, technical know-how, and skill in building teams.

For Thinking Machines Lab, Weng’s departure is the latest of many. Business Insider, in May, reported that nearly a third of the company’s original founding members had left the startup since it launched.

Of the startup’s six cofounders, only two remain: Mira Murati, the CEO, and chief scientist John Schulman. Barret Zoph and Luke Metz left for OpenAI, while Andrew Tulloch left for Meta. Zoph left OpenAI in June, The Verge reported.

Mira Murati, the former OpenAI CTO who leads the startup, thanked Weng for her service on X after she announced her departure on Monday.

“We’ll miss you, it’s been wonderful building Thinky together,” Murati wrote. “I’m glad that you’re putting your health first. Thank you for everything.”

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