Actually, they are using Voxel Global Illumination (VXGI) which seems to be very similar to Sparse Voxel Octree Global Illumination (SVOGI) which was first published by Cyril Crassin of NVIDIA in 2011.
In 2011, NVIDIA engineers developed and demonstrated an innovative new approach to computing a fast, approximate form of global illumination dynamically in real time on the GPU. This new GI technology uses a voxel grid to store scene and lighting information, and a novel voxel cone tracing process to gather indirect lighting from the voxel grid. NVIDIA’s Cyril Crassin describes the technique in his paper on the topic and a video from GTC 2012 is available here. Epic’s ‘Elemental’ Unreal Engine 4 tech demo from 2012 used a similar technique.Since that time, NVIDIA has been working on the next generation of this technology—VXGI—that combines new software algorithms and special hardware acceleration in the Maxwell architecture.
VXGI is not a Direct3D 12 specific feature, in fact, SVOGI it was first implemented in OpenGL 4.x and Direct3D 11. Though the technology has (mostly) been available for years, NVIDIA's Maxwell graphics architecture is the first of its kind to have "built-in" support for the technology.