Lilian Weng, cofounder of Thinking Machines Lab, announced her resignation on July 27, 2026, due to health issues worsened by the intense stress and pace of startup life [1, 2]. She told colleagues and followers on X that she had been sick more in the past seven months than ever before, and said, "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" [1, 2, 3, 4]. Weng added, "I don't feel I'm able to continue at the pace a startup requires." [1]
Since Thinking Machines Lab's 2025 launch, the company has seen the departure of multiple founding members. Of the original six cofounders, only CEO Mira Murati and chief scientist John Schulman remain [2, 5]. Murati, herself a former OpenAI CTO, expressed support for Weng's decision, tweeting, "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." [1, 2, 5]
Weng previously worked at OpenAI from 2018 to late 2024 as vice president of AI safety research, where she helped build the Applied AI Research team [1, 5]. On July 29, OpenAI confirmed Weng would rejoin the company to lead a top-level research team focused on advancing internal research and driving recursive self-improvement of AI systems [1, 6, 5]. Weng said she desired "a scoped role in a more predictable place, and not as a cofounder," noting a calmer work environment suited her better [5].
Weng's experience reflects a recent trend of high-profile AI leaders stepping back from full-time roles due to health concerns, including OpenAI CEO Fidji Simo and xAI cofounder Greg Yang [2, 7]. Industry executives have acknowledged the intense pressures of AI startups. Stability AI founder Emad Mostaque said, "Working at an AI startup is so hard. I got real sick at Stability AI before leaving and finding my balance" [4]. Elastic VP of AI Han Xiao added, "If you work in a team and feel if you're the one carrying everything, that's probably not on you, that's a broken team. You'll burn out every single day and still feel lost" [4].
Weng’s transition comes amid Thinking Machines Lab’s ongoing leadership changes and increasing pressure in the AI sector. She will now focus on leading OpenAI’s internal research efforts, starting immediately following her return.
