Thinking Machines Co-Founder Lilian Weng Steps Down and Returns to OpenAI

Lilian Weng, a co-founder of Thinking Machines, has left the AI startup after citing health concerns and is returning to OpenAI, where she previously served as vice president of AI Safety Research.

Weng announced her departure from Thinking Machines this week, explaining in an internal Slack message, which she also shared publicly on X, that she could no longer maintain the workload required by a fast-moving startup.

“I don’t feel I’m able to continue at the pace a startup requires,” Weng wrote. She said months of sustained stress and workload had reached a level that her health could no longer physically support.

On Wednesday, OpenAI announced that Weng would rejoin the company.

Weng will lead an OpenAI research team.

An OpenAI spokesperson said Weng will lead a top-level team focused on accelerating thecompany’ss internal research efforts.

The team is expected to support research across OpenAI, including work related to recursive self-improvement, an approach in which an AI system helps improve or iterate on itself to become increasingly capable.

Weng’s decision to join OpenAI shortly after leaving Thinking Machines may appear at odds with her concerns about the demands of startup life. However, her responsibilities could differ significantly at an established AI company where she is not serving as a co-founder.

The move is particularly notable as leading AI companies continue competing aggressively to recruit and retain prominent researchers.

Mira Murati supported Weng’s departure.

Thinking Machines co-founder and former OpenAI CTO Mira Murati publicly responded toWeng’ss announcement earlier this week, expressing support for her decision to prioritise her health.

“We’ll miss you; it’s been wonderful building Thinky together. I’m glad that you’re putting your health first. Thank you for everything,” Murati wrote in response to Weng’s post on X.

It remains unclear whether Murati knew at the time that Weng was planning to return to OpenAI.

Weng’s move brings a prominent AI safety researcher back to OpenAI while Thinking Machines loses one of its co-founders amid increasingly intense competition for experienced AI research talent.