Thinking Machines Lab Cofounder Lilian Weng Steps Down Citing Stress and Illness

Lilian Weng, a co-founder of Thinking Machines Lab, has announced she is leaving the AI startup due to stress and illness.

In a post on X, Weng said Tuesday would be her last day at the company, which she co-founded with OpenAI's former chief technology officer, Mira Murati.

Weng, previously OpenAI's vice president of research and safety, stated she had been ill more often in the past seven months than at any other point in her life. She did not disclose a specific diagnosis.

"Despite all the laughter and challenges building a neolab has brought us, I don't feel I'm able to continue at the pace a startup requires," Weng wrote in a message she said she had shared with colleagues at the company, known internally as Thinky.

She added that the "amount of consistent stress and workload have pushed me beyond what my health can sustain physically."

Weng said she tried to rest and take proper sick leave while Thinking Machines was "sprinting" to release Inkling, the company's first open-weight model, but felt "guilt."

She also considered a narrower role that would cause less anxiety but decided it was not a fit. "If I cannot give it 100% for what I should be responsible for, I fail my job," she wrote.

Instead, Weng said she would seek a more predictable, scoped role outside a co-founder position while remaining in AI.

"We'll miss you, it's been wonderful building Thinky together," wrote Murati in a reply on X. "I'm glad that you're putting your health first."

AI Execs Prioritize Health

Weng's departure follows several recent health-related step-backs by leaders in the AI industry.

• Earlier this month, Fidji Simo stepped down from her full-time role as OpenAI's CEO of AGI after a flare-up of postural orthostatic tachycardia syndrome (POTS). Simo moved into a part-time advisory role and said she would focus on recovery from the chronic illness.

• In January, xAI co-founder Greg Yang said he had moved into an informal advisory role after doctors diagnosed him with Lyme disease. Yang said months of unexplained fatigue had left him with less energy and creativity, and that he wanted to "go founder mode on my health."

Weng's departure also comes as Thinking Machines Lab has lost a significant share of its founding team amid Silicon Valley's AI talent war.

A Business Insider review in May found that 13 of the startup's 42 founding members had left since launch, including three of its six co-founders, as rivals — including Meta and OpenAI — offered huge compensation packages.