http://www.techradar.com/news/amds-radeon-rx-vega-now-only-supports-two-graphics-cards-for-multi-gpu-setups

AMD has confirmed that its new Radeon RX Vega graphics cards won’t support any more than two cards in a multi-GPU (previously known as CrossFire) configuration, ruling out the possibility of three- or four-way setups when it comes to gaming.

You will, however, still be able to link up the power of three or four cards when it comes to general computing usage.