Thinking Machines cofounders Barret Zoph and Luke Metz are leaving the fledgling AI lab and rejoining OpenAI, the ChatGPT-maker announced on Wednesday. According to the memo from Simo, Zoph told Thinking Machines CEO Mira Murati on Monday he was considering leaving. A third Thinking Machines staffer, Sam Schoenholz, is also rejoining OpenAI, per the company’s announcement. The departures are a blow to Thinking Machines, which also lost another co-founder, Andrew Tulloch, in November when he took a new job at Meta. Zoph and Metz left OpenAI in late 2024 to start Thinking Machines with Murati, the ChatGPT maker’s former chief technology officer.