Pretty sure this is the voxel GI he blogged about in November of last year. Or it’s what it evolved into. ‘SDFGI’ is Signed Distance Field Global Illumination. Signed Distance Fields are basically a voxelized representation of the 3D geometry, as you can see when he turns on the SDF Cascades view. As he said in the November Vulkan report they’re using a ‘very clever voxel lighting implementation using signed distance fields.’
The thing that’s interesting about this implementation is that the distance field representation gets its colouration from the materials of the object, which allows it to be used for pretty convincing reflections, and the distance fields don’t seem to be stored on a per-object basis with a fixed resolution, as in Unreal’s distance fields (though maybe they are and he just didn’t want to bother showing that part of the process).
I feel like that’s gotta come with a performance cost, if the distance fields are being generated at runtime, or even in real-time. If it can only run at 60fps on a 1060, it might not be suitable for VR, which would be a shame.