Andrej Karpathy, Tesla’s head of AI and a key leader in the development of Autopilot, its driver assist feature which requires supervision by a human, announced on Twitter Wednesday that he’s leaving the company.

“It’s been a great pleasure to help Tesla towards its goals over the last 5 years and a difficult decision to part ways,” Karpathy wrote. “In that time, Autopilot graduated from lane keeping to city streets and I look forward to seeing the exceptionally strong Autopilot team continue that momentum.” In a follow-up tweet, Karpathy said he has “no concrete plans for what’s next” but wants to revisit “my long-term passions around technical work in AI, open source and education.”

The departure seems to be amicable, as CEO Elon Musk replied kindly to Karpathy on Twitter. In March, Karpathy said that he was on a sabbatical to “rest & travel,” but had said he planned to come back to Tesla this month, according to Bloomberg.

Karpathy joined Tesla in 2017, taking over the top AI job after former Apple executive Chris Lattner’s six-month stint in the post. As AI chief, Karpathy has overseen the growth and development of Tesla’s controversial Autopilot driver assist software, though the software is currently under investigation from the federal government after Teslas using Autopilot crashed into parked emergency vehicles.

Karpathy’s departure follows layoffs of nearly 200 Tesla employees focused on Autopilot.