Publicly, Waymo, the self-driving unit of Google parent Alphabet, says the vast majority of its autonomous vehicle testing is taking place in five cities: Mountain View, California; Austin, Texas; Kirkland, Washington; Phoenix, Arizona; and most recently, Detroit, Michigan. But it would seem the company neglected to tell us about a crucial sixth city: its home turf of San Francisco.

TechCrunch obtained pictures of a Waymo autonomous minivan on the fog-soaked streets of San Francisco, forcing the company to admit that it has returned to its city of origin, where it first began testing back in 2009. A Waymo spokesperson did not immediately respond to a request for comment.

It’s a significant move for a couple reasons. The addition of San Francisco to its roster of test cities is a sign that Waymo is interested in tackling denser, more congested urban streets after several years of sticking to smaller, more low-slung communities. And it would appear to be a shot across the bow of GM, which has been testing its Cruise autonomous vehicles in San Francisco and plans to eventually launch a public ride-hail program in the city.

Waymo says it has tested its autonomous minivans in 24 cities across the US in an effort to expose its vehicles to a variety of environments, weather, and road conditions. In San Francisco, Waymo will have the chance to deal with heavy fog and the steep hills for which the city is famous, as well as thousands of bicyclists, pedestrians, and really bad drivers.

Last year, the company began testing its minivans on public roads in Arizona without human safety drivers behind the wheel. In the weeks to come, it says it will be opening these vehicles to the members of its Early Rider program for a ride-hailing trips. There’s no word on when this program will expand to other cities.

Update January 12th, 1:36pm ET: A spokesperson for Waymo said, “San Francisco was one of the first cities where we tested our self-driving cars, dating back to 2009 when we traveled everything from Lombard Street to the Golden Gate Bridge. Now that we have the world’s first fleet of fully self-driving cars running in Arizona, the hilly and foggy streets of San Francisco will give our cars even more practice in different terrains and environments.”