I'm not sure of the exact measurements, but the thickness varies from the outer edge (thinner) to the middle (thicker). Based on the the images that I have seen (cut aways) I'd say that the outer edges is around .5 cm~ and the middle is over 1 cm. The mahogony slab that is used is cut flat, and the maple is sculpted.
The natural maple "binding" on many PRS models tells you the thickness of the maple top at the edge of the body. I haven't measured mine, but the thickness of the binding is on the order of 1/4" or so. In addition to the top getting thicker as you move toward the center-line of the body, it is also true that the thickness increases as you move from the neck pup towards the bridge, and is greatest at the bridge itself. As a rough guess, I'd say it maxes out at around a good 3/4", or perhaps 7/8", but that's just from memory.
The videos on this page show the various steps of body construction for PRSi (solid-body, anyway). The maple stock used for the top looks like it's still about an inch thick after planing, but that doesn't say how much is taken off during the CNC "carving". They don't mention dimensions during the videos - my comments are just based on appearances..... (The video showing the CNC machine carving the bottom, and then the top, is very interesting.)