XConnect relies upon Intel's Thunderbolt 3 specification for allowing notebooks and other portable devices to benefit from an external graphics card if wishing to ramp up the device's performance for gaming. The enclosure for the graphics card is said to be "as simple as using a USB flash drive."
AMD has been developing XConnect in conjunction with Razer and the Thunderbolt working group. Razer's Blade Stealth is the first notebook supporting the XConnect technology in conjunction with R9 300 series graphics cards.
Those wishing to learn more about XConnect can visit AMD.com/xconnect. For now though XConnect appears limited to supporting Windows 10 with no signs of near-term Linux support.