What API are they using for interfacing with the GPU (ie. OpenGL, Vulkan, other ) ? I suspect a lot of time is likely to be spent on the CPU side updating vert

What API are they using for interfacing with the GPU (ie. OpenGL, Vulkan, other ) ? I suspect a lot of time is likely to be spent on the CPU side updating vertex and other data and pushing it to the GPU so it would be useful to have some more detail on how they are handling that.