- Lilian Weng, former OpenAI VP of AI Safety and cofounder of Thinking Machines Lab, has resigned citing seven months of health problems worsened by startup stress.
- Weng's resignation makes her the fourth of six original cofounders to leave the company since its launch in February 2025, raising questions about retention and culture at the $12 billion startup.
- In a note shared with the team, Weng stated she had been sick more in the past seven months than at any other point in her life and that the startup-level pace had made things worse.
- Mira Murati, CEO of Thinking Machines, responded to Weng's resignation by expressing that she was glad Weng was putting her health first.
- Thinking Machines shipped its first open-source model, Inkling, on July 15, just two weeks before Weng's departure.
- Thinking Machines was launched in February 2025 with six cofounders and a vision for enterprise AI that adapts to individual businesses.
- Andrew Tulloch left for Meta in October 2025, while Barret Zoph and Luke Metz departed in January 2026, both returning to OpenAI.
- Zoph's exit reportedly turned acrimonious after he was fired for sharing confidential company information with competitors.
- Thinking Machines raised $2 billion at a $12 billion valuation, making it one of the most richly funded AI startups before shipping anything publicly.
- According to reporting by Fortune and TechCrunch, the departures from Thinking Machines have involved money, compute constraints, and a lack of clarity on products and business model.
Lilian Weng's resignation from Thinking Machines Lab highlights the intense pressures faced by startup employees.1
In her resignation note, Weng stated, "I've been in sickness more than what I've ever experienced in my life", attributing her health decline to the demanding pace of startup life.
Weng is the fourth cofounder to leave the company, which launched in February 2025, following Andrew Tulloch, Barret Zoph, and Luke Metz.678
CEO Mira Murati expressed her support, saying, "I'm glad that you're putting your health first".
The departures raise concerns about the company's culture and retention strategies, especially given that Thinking Machines has raised $2 billion at a $12 billion valuation, making it one of the most richly funded AI startups.10
Weng's experience reflects a broader trend in the tech industry, where the demands of startup life can lead to significant health issues.
As Weng noted, "Life is a marathon, not a sprint", emphasizing the need for a sustainable work environment.
The company recently launched its first open-source model, Inkling, which is a 975 billion total parameter mixture-of-experts model, just two weeks before her departure.5
The ongoing challenges at Thinking Machines, including money, compute constraints, and a lack of clarity on products, have been cited as factors in the cofounders' exits.
“Weng's resignation follows seven months of health problems exacerbated by the startup's demanding pace, raising concerns about retention and culture at the $12 billion company. CEO Mira Murati expressed support for Weng's decision, emphasizing the importance of prioritizing health over work commitments.”
Startup Fortune
