Boston, Massachusetts-based self-driving car startup nuTonomy made headlines in 2016 when it launched the world’s first self-driving taxi service. Albeit a trial only, the service, which covered a few streets in Singapore, provided an early look at a likely future where self-driving cars run around town offering rides.

Now nuTonomy’s self-driving taxi service is up and running in Boston. Since December 6, Lyft users have been able to experience a ride in one of nuTonomy’s self-driving prototypes in Boston’s Seaport district. There are only five of the prototypes, and each still has an engineer behind the wheel in case of an emergency, plus a second engineer to monitor the car’s self-driving system.

nuTonomy, which was bought by automotive supplier Delphi in November for $450 million, partnered with Lyft in June to understand and optimize the user experience of a self-driving taxi service. The company says it has two main goals with the project. The first is to let members of the public experience driverless cars firsthand and become accustomed to the technology. The second is to gather feedback that can be used to adapt and improve the self-driving taxi service.

Lyft is also closely linked with General Motors which bought a $500 million stake in the ride-sharing company in 2016. The deal between GM and Lyft wasn’t exclusive, though, which is why we’ve seen Lyft partner up with a number of other firms since then, including direct rivals to GM such as Ford. GM has also launched its own initiatives that could be seen as a threat to Lyft, such as the Maven car-sharing service.

Making the partnership between Lyft and GM murkier is the fact that both firms are working on their own respective self-driving taxi services. GM is developing its service with Cruise Automation, which the automaker fully acquired in 2016. Lyft meanwhile is working with a startup by the name

Neither GM nor Lyft has said when it will have a self-driving taxi service similar to the one being offered by nuTonomy. Meanwhile, Alphabet said in November that its Waymo unit will have a self-driving service available in Phoenix, Arizona within months. Waymo’s service is expected to run without a human behind the wheel, though an engineer will still be in the vehicle to monitor things and stop the car at a push of a button if necessary.