On July 28, Lilian Weng, co-founder of the U.S.-based AI unicorn Thinking Machines Lab and the ex-Vice President of Research and Safety at OpenAI, took to the X platform to announce her resignation. In her heartfelt resignation letter, Weng revealed that she had been plagued by frequent illnesses over the past seven months, a direct consequence of relentless stress and a workload that had surpassed her physical limits.

A proud graduate of Peking University, Weng embarked on her journey with OpenAI in 2018, where she played a pivotal role in ensuring the safety of models like GPT-4. Her dedication and expertise led to her promotion to Vice President of Research and Safety in 2024. In February 2025, she further expanded her horizons by co-founding Thinking Machines Lab. Despite her enduring passion for AI, Weng expressed a desire to transition to an organization that offers a more predictable work pace and clearer responsibilities for the next chapter of her career.