Waymo is making its ride-hailing app more widely available by putting it on the Google Play store as the self-driving car company prepares to open its service to more Phoenix residents.

The company, which spun out to become a business under Alphabet, launched a limited commercial robotaxi service called Waymo One in the Phoenix area in December. The Waymo One self-driving car service, and accompanying app, was only available to Phoenix residents who were part of its early rider program, which aimed to bring vetted regular folks into its self-driving minivans.

Technically, Waymo has had Android and iOS apps for some time. But interested riders would only gain access to the app after first applying on the company’s website. Once accepted to the early rider program, they would be sent a link to the app to download to their device.

The early rider program, which launched in April 2017, had more than 400 participants the last time Waymo shared figures. Waymo hasn’t shared information on how many people have moved over to the public service, except to say “hundreds of riders” are using it.

Now, with Waymo One launching on Google Play, the company is cracking the door a bit wider. However, there will be still be limitations to the service.

Interested customers with Android devices can download the app. Unlike a traditional ride-hailing service, like Uber or Lyft, this doesn’t mean users will get instant access. Instead, potential riders will be added to a waitlist. Once accepted, they will be able to request rides in the app.

These new customers will first be invited into Waymo’s early rider program before they’re moved to the public service. This is an important distinction, because early rider program participants have to to sign non-disclosure agreements and can’t bring guests with them. These new riders will eventually be moved to Waymo’s public service, the company said. Riders on the public service can invite guests, take photos and videos and talk about their experience.

“These two offerings are deeply connected, as learnings from our early rider program help shape the experience we ultimately provide to our public riders,” Waymo said in a blog post Tuesday.

Waymo has been creeping toward a commercial service in Phoenix since it began testing self-driving Chrysler Pacifica minivans in suburbs like Chandler in 2016.

The following year, Waymo launched its early rider program. The company also started testing empty self-driving minivans on public streets that year.

Waymo began in May 2018 to allow some early riders to hail a self-driving minivan without a human test driver behind the wheel. More recently, the company launched a public transit program in Phoenix focused on delivering people to bus stops and train and light-rail stations.