If anyone was curious about what Rivian's brake calipers look like off the R1S and R1T here you go!
Due to the performance and weight of these vehicles, I am sure they didn't skimp on these brakes.
I think the type of brakes also depends on how much of the braking is done by the regen.Eh, don't kid yourself, ever see what stops the 2500 and 3500 series trucks? Nothing fancy, just cheap and reliable.