VTK-h is a toolkit of scientific visualization algorithms for emerging processor architectures. VTK-h bring together several projects like VTK-m and DIY2 to provide a toolkit with hybrid parallel capabilities.
Both Ascent and VTK-h use a specific version of VTK-m. For the current version see:
https://ascent.readthedocs.io/en/latest/BuildingAscent.html#vtk-m-optional-but-recommended
Or
https://github.com/Alpine-DAV/ascent/blob/develop/hashes.txt
VTK-h's source is hosted on GitHub:
https://github.com/Alpine-DAV/vtk-h
VTK-h is released under 3-clause BSD license.