While checking some reviews of the AMD Radeon RX 480, I noticed that Ryan Shrout from PC Perspective discusses that AMD built only a single reference design card to cover both the 4GB and 8GB varieties. According to him, all 4GB reference cards from AMD actually have 8GB memory onboard, they just have a different BIOS.
It's really strange and I have trouble believing this will apply to all retail cards. But if this is true, there will likely be a hack soon that will turn 4GB cards into 8GB models.
Another oddity – and one that may make enthusiast a bit more cheery – is that AMD only built a single reference design card for this release to cover both the 4GB and 8GB varieties. That means that the cards that go on sale today listed at 4GB models will actually have 8GB of memory on them! With half of the DRAM partially disabled, it seems likely that someone soon will find a way to share a VBIOS to enable the additional VRAM. In fact, AMD provided me with a 4GB and an 8GB VBIOS for testing purpose. It’s a cost saving measure on AMD’s part – this way they only have to validate and build a single PCB.