Well the math says they won't. If the most a rider can pay is $10, and if Lyft takes a cut, then the max the driver will receive will be less than $10, which is not what they say.

It says "drivers earn up to $10 per trip", which means a driver can earn nothing! Or the rider can pay "from $4-10"; Lyft takes no more than the rider(s) pay; and the driver takes the rest.

The terms of service have a section reserving the right to impose a service fee. Not sure if there will be a fee at launch.

"Service Fee. In exchange for providing the Carpool Platform, Clara Rides may assess a service fee on each Carpool Ride (on either or both of the Carpool Rider or Carpool Driver). The amount of the applicable service fee shall be communicated to you in writing."

If 3 riders paid $5 each and Lyft took one third of that, the driver would get $10.