The RX 490 is a dual GPU graphics card
All of these things indicate to us that we are looking at a dual GPU solution, probably one based on a full version of Polaris 10. The only other alternative was that the C99 variant is Vega 10 but there are some gaping holes in that theory that in my opinion put it at negligible probability: 1) Vega 10 by recent reports is too early in the development stage to have made it out to the FOC testing phase. In fact, if I were to offer some proof: the C99 board passed RRA certification on 8th April 2016 which was way before AMD celebrated the Vega 10 GPU development milestone! 2) The nomenclature indicates to a Polaris card.
So we know for a fact that the C99 board has yet to be accounted for. We know that its value is equal to roughly double of the RX 480. We know that the nomenclature indicates a Polaris GPU yet Polaris 10 is the full fat chip (meaning there isn’t a more powerful Polaris variant out there) and finally, that it passed RRA certification way before Vega 10 was anywhere near completion. In fact, the only way the RX 490 ends up being a Vega 10 GPU is if it arrives next year (which would mean that the C99 board will be called something else), which doesn’t make a lot of sense considering its (RX 490) listing has popped up in AMD partner AIB sites as well.