After months of unexplained fatigue, an xAI cofounder says he’s stepping back from the company following a Lyme disease diagnosis.
Greg Yang said in a post on X published Tuesday that he will move into an informal advisory role at Elon Musk’s startup xAI immediately so he can “go founder mode on my health.”
Lyme disease is a bacterial infection typically transmitted by ticks and is known for symptoms that can linger or worsen over time.
Yang said his symptoms began after an illness in early 2025, when he noticed lingering fatigue and a drop in energy and creativity weeks after he believed he had recovered.
Over time, the symptoms worsened, with workouts or certain foods leaving him exhausted for days, he said.
“There was a week where I slept 12 hours a day and still couldn’t recover,” he added.
After multiple rounds of testing, Yang said his doctor diagnosed him with Lyme disease, a condition that is “famously hard to diagnose.”
He said that he was surprised by the diagnosis, as he did not recall a tick bite.
“Likely I contracted Lyme a long time ago, but until I pushed myself hard building xAI and weakened my immune system, the symptoms weren’t noticeable,” he added.
Despite the setback, Yang said he felt “lucky” to have caught the condition relatively early. He said discovering it now would allow him to “fix it so I can push myself even harder when I rebound.”
In response to Yang’s X post, Musk replied that he hoped Yang would “get well soon.”
“Maybe Grok will find a cure!” Musk added.
Yang joined xAI as a cofounder in June 2023, after spending nearly six years as a researcher at Microsoft, according to his LinkedIn profile.
Yang’s move comes after two other xAI cofounders, Igor Babuschkin and Christian Szegedy, left the company last year.
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