One thing that strikes me is how it evolves with new features. Not just higher level libraries, but also more fundamental, low level stuff, such as virtual memory, standard memory models, c++ libraries, new compilers, communication with other GPUs, launching dependent kernels, etc.

At their core, OpenCL and CUDA both enable running parallel computing algorithms on a GPU, but CUDA strikes me as much more advanced in terms of peripheral features.

Every few years, I think about writing a CUDA program (it never actually happens), and investigate how to do things, and it’s interesting how the old ways of doing things has been superseded by better ways.

None of this should be surprising. As I understand it, OpenCL has been put on life support by the industry in general for years now.

Developing fast... OpenCL is much harder to learn than CUDA. Take someone who did some programming classes, explain how CUDA works and they'll probably get somewhere. Do the same thing with OpenCL and they'll probably quit.