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.