As it nears the launch of its first commercial service, Waymo is celebrating a new milestone: 10 million miles driven on public roads. In recognition of this threshold, the Alphabet company released a video that features a lot of new footage of its cars operating without a human driver behind the wheel. In addition, Waymo’s top executive is setting realistic expectations about some of the limitations of its advanced technology.

Last November, Waymo announced it had driven 4 million miles on public roads. Then, in July, the company said it had crossed 8 million miles. At the end of August, it hit 9 million miles, so today’s announcement is clearly another sign of Waymo’s aggressive scaling as it prepares to kick off its first ride-hailing service in Phoenix, Arizona, before the end of the year.

The news comes at a time of skepticism around the technology

The news comes at a time of skepticism around the technology. In March, a self-driving Uber vehicle struck and killed a pedestrian while the backup safety driver was streaming a video on her phone, police said. Uber suspended testing in the aftermath, and some safety advocates said the crash showed the system was not yet safe enough to be tested on public roads.

Waymo is clearly the leader in this space, but there is also growing skepticism about its technology. In August, The Information reported that Waymo has been trying to remove human safety drivers from its self-driving cars, but that process has been slower and more challenging than anticipated. The vehicles have trouble making unprotected left turns, for example, and some of the cars have difficulty merging with highway traffic, the site reported, citing unnamed sources. Last week, The Information also reported that a previously disclosed crash was actually caused by a safety driver falling asleep at the wheel and accidentally disengaging the self-driving system. (No injuries were reported.)

In a blog post on Wednesday, Waymo CEO John Krafcik acknowledged that there were still some technical challenges to solve.

“Our driving should feel natural to our riders and others on the road. Today, our cars are programmed to be cautious and courteous above all, because that’s the safest thing to do. We’re working on striking the balance between this and being assertive as we master maneuvers that are tough for everyone on the road. For example, merging lanes in fast-moving traffic requires a driver to be both assertive enough to complete the maneuver without causing others to brake and smooth enough to feel pleasant to our passengers.

The experience of using one of Waymo’s self-driving cars to run errands, for example, is likely to be less convenient than driving yourself or using a human-driven ride-hailing service, Krafcik said. But only at first.

“Today, our cars are designed to take the safest route, even if that means adding a few minutes to your trip,” he said. “They won’t block your neighbor’s driveway and will choose the safest place to pull over, even if it means having to walk a few extra steps to a destination.”

“our cars are designed to take the safest route, even if that means adding a few minutes to your trip.”

Waymo also posted a video of an upbeat interview with Nathaniel Fairfield, principal software engineer at the company. The video features plenty of shots of Waymo’s self-driving Chrysler Pacifica minivans operating on public roads without a driver behind the wheel, which seems like an effort to rebuff reports that it is still using safety drivers in the majority of its testing. Also, see Waymo’s driverless cars navigate tricky situations, like snowy roads, dust storms, and that time a ball went into the street!

“Today, our vehicles are fully self-driving, around the clock, in a territory within the Metro Phoenix area,” Krafcik writes. Previously, Waymo said its robot taxi service will be “fully driverless” at launch, which the company promises will take place before the end of the year. The clock is ticking.

Update December 5, 2018 8:15AM ET: This article was originally published on October 10, 2018 and has been updated to include video.