Lilian Weng, a co-founder of Thinking Machines, is leaving the startup and rejoining OpenAI, the company told TechCrunch on Wednesday.
Weng said earlier this week that she was stepping down from Thinking Machines because of health issues, according to an internal Slack message she also shared on X.
“I don’t feel I’m able to continue at the pace a startup requires,” Weng wrote. “After thinking about it for several months, I ultimately have to admit that the amount of consistent stress and workload have pushed me beyond what my health can sustain physically.”
It is a hard and sad decision. I shared this message with folks at Thinky. Thank you all for the time together
Just as the last sentence in my message: The future worth building is human. pic.twitter.com/VGb5fM5chX
— Lilian Weng (@lilianweng) July 27, 2026
OpenAI told TechCrunch that Weng previously served at the company as vice president of AI Safety Research. A company spokesperson said Weng will lead a top-level team focused on accelerating OpenAI’s internal research.
According to the spokesperson, the team will support cross-research work on recursive self-improvement, which would allow an AI system to iterate on itself to become more powerful.
Thinking Machines co-founder and former OpenAI Chief Technology Officer Mira Murati said on X that she supported Weng’s decision to prioritize 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.
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