Less than a week after Thinking Machines cofounder Lilian Weng resigned citing stress and illness, she is rejoining Sam Altman

Less than a week after announcing her resignation from Thinking Machines Lab citing stress and illness, cofounder Lilian Weng is now returning to work alongside OpenAI CEO Sam Altman. According to a report by Business Insider, Weng, who previously served as 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. In her farewell post, she explained that the “consistent stress and workload” of building a startup had pushed her beyond what her health could sustain.Weng’s departure came as Thinking Machines was sprinting to release its first open-weight model, Inkling. She admitted feeling “guilt” about taking sick leave during that critical period and considered narrowing her role before deciding to step away entirely. “If I cannot give it 100% for what I should be responsible for, I fail my job,” she wrote. But just days later, Weng has chosen to rejoin Altman in a scoped role that promises more predictability and less strain than her cofounder responsibilities. A report by TechCrunch revealed that OpenAI has confirmed that Weng will be joining the company as the VP of AI Safety Research. “I’ve always been a curiosity-driven person. Leaning new knowledge or figuring out how to solve problems that are not well defined often gives me simple joy. The fun part of being a cofounder is how it “forced” me to develop new perspectives on company strategies, team building (at the company level), and much more, as well as how these seemingly abstract terms are deeply connected with our day-to-day actions, planning and narratives. With real-world experience, ideas that once felt theoretical become approachable and it is true for many terms in many domains,” wrote Weng in a post on X.Mira Murati the founder of Thinking Machines Lab thanked Weng for everything. “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.”

Health challenges among AI leaders

Her move follows a string of health-related step-backs across the AI industry. Earlier this month, Fidji Simo left her full-time role as OpenAI’s CEO of AGI after a flare-up of POTS, while Greg Yang of xAI shifted into an advisory role after being diagnosed with Lyme disease. The pressures of leading frontier AI labs have increasingly highlighted the toll on executives’ health.Thinking Machines itself has been hit hard by Silicon Valley’s AI talent war. A Business Insider review found that 13 of its 42 founding members have left since launch, including three of its six cofounders, as rivals like Meta and OpenAI offered lucrative compensation packages. Weng’s return to Altman underscores how talent continues to circulate among the most influential players in AI.