We suspect that AMD has physically removed the additional piping that was put in place to run the RX 7900 XTX's 384-bit wide memory bus, which would also explain the redesigned PCB. The RX 7900 GRE features a 256-bit wide memory bus, which is significantly narrower compared to the RX 7900 XTX. As a result, removing two MCDs worth of piping is probably how AMD shrunk Navi 31 so much.
What's particularly curious is that AMD's
RX 7900 GRE specifications page lists 54 billion transistors for the new chip. The
RX 7900 XTX and
RX 7900 XT page meanwhile list 58 billion transistors. It could just be a typo, but clearly there's more going on behind the scenes than might otherwise be immediately apparent.
Physically altering a GPU package like AMD has done with the RX 7900 GRE isn't too difficult, but altering the die would be very unusual — that takes a lot of money and time to pull off. We cannot be sure of AMD's exact changes or the reasons for the changes. Regardless, it would be very odd for AMD to go through all this hassle for one SKU that's limited to China.
We expect this revised Navi 31 will show up in some other GPU models down the road, possibly in the RX 7800 series and/or mobile GPU equivalents. Meanwhile, Navi 32 GPUs have not yet shown up.