There’s a new option in the config.lua to allow you to specify whether or not you have a Crossfire or SLI setup. If you enter the game and quit out at the menu, the config.lua should have this new option available, ‘multi_gpu = false’. Set this to true to enable multi gpu support.
If you’re running a Crossfire setup you will need to enable Crossfire for the game in the AMD control center.
There are still other issues with Crossfire/SLI support that we are aware of and aiming to iron out soon.