Lilian Weng, who cofounded Thinking Machines Lab with OpenAI's ex-CTO Mira Murati, said consistent stress and workload pushed her beyond what her health could sustain.
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A cofounder of Thinking Machines Lab is leaving the AI startup, citing the toll of stress and illness.
Lilian Weng, who helped launch the company with former OpenAI chief technology officer Mira Murati, said Tuesday would be her last day. In a post on X, Weng – previously OpenAI's vice president of research and safety – said 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 said 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 sick leave while Thinking Machines was "sprinting" to release Inkling, the company's first open-weight model, but felt guilt. She said she had 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 cofounder position while staying in AI.
"We'll miss you, it's been wonderful building Thinky together," Murati wrote in a reply on X. "I'm glad that you're putting your health first."
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. Simo moved into a part-time advisory role and said she would focus on recovery. In January, xAI cofounder Greg Yang said he had moved into an informal advisory role after doctors diagnosed him with Lyme disease, citing months of unexplained fatigue.
The 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 cofounders, as rivals including Meta and OpenAI offered large compensation packages.
Weng said her message to colleagues ended with the line: "The future worth building is human."
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