Lilian Weng Leaves Thinking Machines Lab — the Fourth Co-Founder Exit From a Six-Person Founding Team, Citing Seven Months of Health Problems
Lilian Weng on X (corroborated by OfficeChai, KuCoin, 36Kr, Digg)via @lilianweng·medium signal
Lilian Weng announced on 2026-07-27 that she is leaving Thinking Machines Lab with July 29 as her final day, publishing the note she sent internally. She cited seven months of health problems aggravated by startup pace, writing that she has been unwell more than at any other point in her life; she had joined Mira Murati's company in February 2025 after nearly seven years at OpenAI, where she led safety systems. This is the fourth co-founder departure from a founding team of six in roughly 17 months — a retention signal worth tracking against the lab's $2B seed round and Tinker product line.