The top tech leader for Google Inc.’s self-driving car unit, Chris Urmson, has left the company amid reports that he disagreed with the direction of the project.

In a post on Medium, Urmson (pictured above), the unit’s chief technology officer and technical lead, didn’t provide a reason for the departure or what he might be doing next. Google could not be reached immediately for comment.

“I have every confidence that the mission is in capable hands,” he wrote. “I will be cheering along and following their progress.”

However, the New York Times reported that Urmson had argued with Larry Page, chief executive of Google parent company Alphabet, about unnamed changes in the project’s direction several months ago. Last September, former Hyundai America Chief Executive Officer John Krafcik was appointed to head the project.

That was viewed as a sign that the autonomous car project, which has been part of the X “moonshots” group at Alphabet, was expected to be spun out into a separate company. X chief Astro Teller said recently it was close to being ready to “graduate” from X. But it’s still not clear when the unit might have a commercial product – likely not for several years – or what its business model will be.

Last December, reports surfaced that Google was teaming up with Ford Motor Corp. on autonomous cars. Details of the reported arrangement were scarce, but in April, the two companies joined forces to lead a coalition dedicated to getting federal approval for autonomous cars.

Two other members of the car unit have left too. The Times reported that a software lead, Dave Ferguson, has left along with Jiajun Zhu, one of the team’s founders and leader of the creating the car’s perception technologies and its large scale simulation system, to form a new startup. Recode reported that Zhu’s LinkedIn profile listed a new role as a startup co-founder, but the profile currently lists only his current Google role.

Urmson had taken over leadership of the unit two years ago when Sebastian Thrun, a founder of the car project and of Google X, left the company. The other project founder, Anthony Levandowski, left earlier this year to start Otto, a started aiming to retrofit freight hauling trucks with self-driving technology, along with former Google, Apple and Tesla employees.

Apple Inc. also recently switched leaders for its own autonomous car project, according to the Wall Street Journal.

Despite reports of tension, Google and Urmson alike sought to downplay any friction. “Chris is an incredible colleague & leader,” Krafcik tweeted. “Thank you for your passion & humility. Good luck on your new adventures!”

For his part, Urmson said in his post that he’s looking at different challenges. “Now, 1.8 million miles of autonomous driving later, I’ve decided the time is right to step down and find my next adventure,” he wrote. “I am ready for a fresh challenge.”

Photo from Chris Urmson/Medium