What started out as a temporary pilot project to test a robotaxi service in Las Vegas has turned into a multi-year partnership between self-driving software company Aptiv and Lyft and a new milestone that suggests the operation is ramping up.

The companies announced Tuesday that they’ve given 100,000 paid rides in Aptiv’s self-driving vehicles via the Lyft app.

“To our knowledge, this is the largest open-to-the-public commercial pilot,” Aptiv Autonomous Mobility President Karl Iagnemma said in a recent interview. “To me this partnership is a great example of the next-generation ecosystem at work.”

The milestone has a few important caveats. Aptiv’s self-driving vehicles — which initially began with BMW 5 series — have a human safety driver behind the wheel to take over if needed. The human driver operates the vehicle manually in parking lots and hotel lobby areas.

The program, even if with those human safety drivers behind the wheel, has proven invaluable to the companies, according to Iagnemma and Jody Kelman, who leads the self-driving platform team at Lyft.

“We’ve got something here,” Kelman said. “This is really a blueprint for what future mobility partnerships can look like.”

Companies in this so-called “race” to commercially deploy on-demand ride-hailing services using self-driving vehicles must master more than the technical bits. Fleet management, real-time routing and designing an approachable user interface are just a few critical components needed to operate a profitable robotaxi service.

The program has taught Aptiv how to “get and keep a fleet of autonomous vehicles on the road and keep them highly utilized,” Iagnemma said, later adding that this project positions Lyft and Aptiv to be major winners in this space. The companies also learned how to work with various regulatory bodies, in this case, with the city of Las Vegas, Clark County and the region’s transit authority.

Lyft and Aptiv first launched the pilot in January 2018 as a one-week experiment and then announced plans to extend the program. The program surpassed 5,000 self-driving rides by August and jumped to more than 25,000 paid autonomous rides by December 2018, all while maintaining an average passenger rating of 4.95 out of five stars, Aptiv said at the time.

By May 2019, the companies reported they had given more than 50,000 paid self-driving rides in Las Vegas.

Aptiv’s investment in Las Vegas expanded as those ridership numbers grew. The company opened in December 2018 a 130,000-square-foot technical center in the city to house its fleet of autonomous vehicles as well as an engineering team dedicated to research and development of software and hardware systems, validation and mapping.