The self-driving car project started by George Hotz, the first person to ever unlock the iPhone, has been canceled. The project involved a $999 after-market kit called “Comma One” that was capable of adding semi-autonomous capabilities to Honda Civics and some Acura cars. Hotz canceled the product after the National Highway Traffic Safety Administration (NHTSA) sent his company, Comma.ai, a letter expressing concern that the product “would put the safety of [Comma.ai’s] customers and other road users at risk.”

Hotz posted the full letter (which you can read here) to the Comma.ai Twitter account this morning. It was sent alongside a special order requesting more information about the Comma One, and The Verge was able to confirm its authenticity. Hotz also wrote that he “would much rather spend my life building amazing tech than dealing with regulators and lawyers. It isn't worth it.” He went on to write that he was canceling Comma One, and that Comma.ai “will be exploring other products and markets.”

Comma.ai will now explore “other products and markets”

The letter from the NHTSA didn’t expressly demand or request that Hotz shut down the Comma One project. Rather, the government agency said in the letter that it “strongly encourage[s]” Comma.ai to either delay selling or deploying Comma One on public roads “until [Comma.ai] can ensure it is safe.”

Hotz famously got in a public spat with Tesla CEO Elon Musk over their respective approaches to self-driving cars. But for all of Hotz’s bluster, he had at least been willing to admit to Comma One’s limits. As recently as last week he wrote a blog post saying that Comma One “will not turn your car into an autonomous vehicle. It is an advanced driver assistance system.”

The NHTSA references this blog post in its letter, and expressed particular concern that users would try to push Comma One beyond those limits — much like has happened with Tesla’s Autopilot feature. “As you are undoubtedly aware, there is a high likelihood that some drivers will use your product in a manner that exceeds its intended purpose,” Paul A. Hemmersbaugh, NHTSA’s chief counsel, writes. “This creates a safety risk to drivers using your product than their passengers and other road users because the vehicle may not respond as expected if it is operating in a manner for which it is not designed.”

NHTSA didn’t explicitily ask Hotz to shut down Comma One

We took a ride in a car equipped with an early version of Comma One this summer, and it was a bit of a mixed bag. It handled lanes well on the highway, but had some trouble with on- and off-ramps. The system was less sure of itself in city driving situations.

We’ve reached out to both the NHTSA as well as Hotz and the Comma.ai team for comment and will update this post when they respond.

Correction: This story previously identified George Hotz as the first person to jailbreak the iPhone. Hotz was the first person to carrier-unlock the device.