ok, after spending too much time on the phone with two different dealerships...
The GSX front calipers are two piston, and the rotors are 1 inch larger than the other models (all of the other models have the same)
The GSX rear brakes are the same as the rest of the models. single piston caliper, same size rotors.

So the GSX upgrade consists of replaces the front rotors and calipers.