VXGI on OpenGL.

In 2015, the OpenGL port of VXGI (Voxel based Global Illumination) was said to be a few months out.
Is it available yet?
On the VXGI download link, there is only a DirectX version listed?

UPDATE: Ok, the windows download includes GL4, DX11, DX12 versions in 32b and 64b.

I noticed that both the DX and GL versions of the Sponza demo fully load a CPU core.
Is this to be expected?
It surprised me as I thought the GPU would be the bottleneck: I run this on a modest GPU.

i5-4570 @3.2GHz

I see this for both VXGI mode and VXAO mode.
All parts of the algorithm run on GPU, so why should the CPU be fully loaded?