Autonomous driving company Waymo has launched its tie-in with Lyft, using a “handful” of vehicles to pick up riders in its Phoenix testing zone, per CNBC. To be eligible, Lyft users requesting a ride have to be doing a trip that both starts and ends in the area of Phoenix that it’s already blocked for for its own autonomous testing.

The number of cars on the road is less than 10, since Waymo plans to eventually expand to 10 total for this trial but isn’t there yet. Those factors combined mean that the number of people who’ll get this option probably isn’t astronomical, but when they are opted in, they’ll get a chance to decide whether to go with the autonomous option via one of Waymo’s vans (with a safety driver on board) or just stick with a traditional Lyft.

Waymo and Lyft announced their partnership back in May, and the company still plans to continue operating its own Waymo One commercial autonomous ride-hailing service alongside the Lyft team-up.