Metal and Apple Silicon
Metal is Apple's graphics-and-compute API, and on Apple silicon it sits on top of a hardware fact that has no real CUDA equivalent: the CPU and GPU are not two devices connected by a bus, they are two sets of cores reading the same physical memory. That single fact changes what "offload to the GPU" even means on this hardware, and it's the reason this page exists separately from the rest of the portability folder rather than being folded into a general graphics-API page alongside Vulkan and DirectX Compute.