Vehicles purpose-built to drive without human help received the first-ever approval in the US to pick up paying customers, the National Highway Traffic Safety Administration (NHTSA) announced on Thursday.

The company, Amazon subsidiary Zoox, says it will soon begin to charge for rides in Las Vegas, where it’s been carrying passengers for free since last year. The company is also currently picking up a limited set of passengers in Austin, Miami, and San Francisco, all for free.

The approval is a milestone for the autonomous vehicle industry. Waymo, the nation’s leading robotaxi provider, uses vehicles that meet government design standards—with steering wheels, pedals, and mirrors, and conventional seating arrangements. (Even the company’s new, purpose-built robotaxi has those legally mandated features.) But some industry players argue that driverless tech can only reach its potential with vehicles built to be driven by computers—ones that don’t meet federal vehicle safety standards written for older technology.

That has proven a difficult path. Zoox has worked for more than a decade to design, manufacture, and receive government approval for its vehicles, which don’t have steering wheels or pedals and feature a “campfire-style” seating arrangement where riders face each other.

The NHTSA’s two-year exemption from its safety standards will allow Zoox to deploy up to 5,000 robotaxis. The company will, in turn, be subject to more stringent government oversight and will submit extra data on crashes and unexplained stops. The NHTSA can retract Zoox’s exemption if it finds that it’s not operating safely.

In a speech at an industry conference in San Diego on Thursday, NHTSA administrator Jonathan Morrison said Zoox had proved that it exceeded the safety standards applied to traditional cars.

“This technology needs to be developed appropriately, safely, and responsibly,” Morrison said to an audience of industry insiders and policy experts. “If we see an unreasonable risk to safety, you’re going to hear from us.”

Earlier this month, Morrison published an unusual open letter drawing attention to what he called a “clear pattern” of autonomous vehicles interfering with the work of emergency responders. “To state it bluntly: An AV that cannot safely interact with first responders is a danger to the general public,” he wrote then, and directed companies to focus their resources on fixing the issue. Morrison said the NHTSA would meet with several companies about their solutions to this emergency response interference issue.

Tesla says it started testing its own steering-wheel-free Cybercab in late June but hasn’t outlined how it might receive government approval for those vehicles. Its limited robotaxi service currently uses modified Model Y’s with steering wheels and pedals.

Zoox says that even before official approval to carry customers, it has autonomously transported more than 500,000 riders more than 3 million miles. The company issued a voluntary recall on its software earlier this month after it found that its cars might not properly detect smoke and could get in the way in emergencies. That government filing indicated that Zoox has 105 active robotaxis—an indication that getting to 5,000 will be a lot of work.