As detailed by Nvidia, the demo is titled "WITCH - Chapter 0 [cry]" and is powered by DirectX 12. The footage shown is allegedly in-game, with each scene comprised of "over 63 million polygons"; six to twelve times more than the capabilities of DirectX 11. Microsoft corporate vice president Steve Guggenheimer showcased the demo, altering lighting effects and camera angles in real-time. The build was shown on a PC running four GeForce Titan X graphics cards.
Square Enix first revealed its Agni's Philosophy Final Fantasy tech demo at E3 in 2012. The four minute video runs off the company's proprietary Luminous Studio Engine, and took twelve months to create.
Nvidia's DirectX 12 API will be included with the upcoming Windows 10. For a technical breakdown of Direct X12's advancements, be sure to read this post on Microsoft's developer website.