Two days ago we posted that Radeon RX 480 cards sold as 4GB model actually have 8GB of GDDR5 memory physically on-board, it's just that 4 GB is BIOS activated. We already mentioned that it should be very possible to flash an 8GB BIOS into the 4 GB one, and get the extra 4GB for free.
The colleagues over at TPU have been able to get their hands on a 4 GB board, and tested that theory. And what do you know, it certainly works:
We first discovered that our 4 GB retail card had the same exact Samsung 8x 8 Gb chips (including the same bin, specc'd for 8 Gbps) as the 8 GB card. We flashed this card with the 8 GB card's BIOS, and were successful in doing so. The trick here is to extract the BIOS of the 8 GB card with ATIFlash 2.74 and then transplanting that BIOS onto the 4 GB card. The 8 GB card BIOS image which we used, can be found here. Use at your own risk.
After the new BIOS was flashed they ran COD Black Ops 3 to confirm the extra 4 GB memory to be working. You not just will get a bump to 8GB of graphics memory, it now runs at 8 GHz (effective data-rate) as well. Also in game (COD caches all memory it can use) the "Memory Usage (dedicated)" completely filled up towards 8GB.
Flashing the reference 4 GB Radeon RX 480 to 8 GB works, if it has 8 GB of memory physically present. And you only know that for sure once you purchased it and can check out the memory ICs.