Do you want to know what's hiding under this enormous heat sink? So do we. After twirling away a few more Torx screws and tossing aside the mounting springs, we have an answer:

One GPU, which sadly is BGA-soldered in place. And at the opposite side, one workstation-class Xeon processor—not soldered in place.

It's too early to say how feasible a CPU upgrade might be—the chip appears to be custom-made for Apple by Intel. But upgrades seem at least theoretically possible.

It might be nice if your $5,000+ workstation could get an upgrade once in a while, rather than a full replacement... right?