xAI has now lost one-fourth of its original founding team, with the latest departure stepping aside because of health concerns.
xAI co-founder Greg Yang has said that he’s stepping aside into an informal advisory role to manage his Lyme disease. “I’ve been suffering from Lyme disease. I’m stepping back from xAI into an informal advisory role so I can go founder mode on my health, starting today,” Yang posted on X.
Yang revealed that debilitating symptoms began appearing in early 2025—including severe fatigue, reduced cognitive function, and extended recovery times from minor activities—which he initially attributed to a common illness. After extensive testing, his doctor diagnosed Lyme disease, which Yang likely contracted years ago but remained asymptomatic until the intense demands of building xAI weakened his immune system.
“Accidentally eating the wrong thing would make me extremely tired, taking days to recover. Working out would leave my whole body feeble for days. There was a week where I slept 12 hours a day and still couldn’t recover,” Yang said.
xAI founder Elon Musk wished Yang well. “Hope you get well soon. Maybe Grok will find a cure!” he posted on X.
Greg Yang becomes the fourth xAI co-founder to depart since the lab was founded in March 2023. The original twelve co-founders included Musk alongside Igor Babuschkin, Yuhuai (Tony) Wu, Kyle Kosic, Manuel Kroiss, Greg Yang, Zihang Dai, Toby Pohlen, Christian Szegedy, Guodong Zhang, Jimmy Ba, and Ross Nordeen. Three had previously departed: Igor Babuschkin left in August 2025 to launch Babuschkin Ventures, a VC firm focused on safe AI; Kyle Kosic departed in 2024 to join OpenAI; and Christian Szegedy also left in 2024 for a role at Morph Labs.