Thinking Machines co-founder Lillian Weng left the company for health reasons and joined OpenAI

Lillian Wing, co-founder of Thinking Machines, announced this week that she is stepping down from her position, citing health issues.

“I don’t feel like I can keep up with the pace that the startup requires,” she wrote in an internal Slack message, which she also shared on X. “After thinking about it for months, I finally have to admit that the amount of constant stress and workload has pushed me beyond what my health can physically handle.”

On Wednesday, OpenAI told TechCrunch that Weng would rejoin the company, where she previously served as vice president of AI safety research.

According to a company spokesperson, Weng will lead a high-level team focused on accelerating OpenAI’s internal research. This team will support joint research work on iterative self-improvement, a process that would allow an AI system to iterate on itself to become more powerful.

The move could be read as a contradiction to Wing’s statements about the impact of working at a fast-paced startup on her health — however, she likely wouldn’t experience the same amount of direct stress while working at a company she’s not a co-founder of. However, at a time of fierce competition for talent among AI labs, this high-profile departure is notable.

Mira Moratti, co-founder of Thinking Machines and former CTO at OpenAI, responded to Weng’s X post earlier this week and expressed support for her decision to focus on her health. It is not clear whether Moratti was aware that Wong would rejoin OpenAI.

“We will miss you, building Thinky together has been amazing. I’m glad you are putting your health first. Thank you for everything,” Moratti wrote in response to Wong’s post.