The AI masking commands should obey the setting of Preferences > Performance > Use Graphics Processor, allowing users to disable its use. That will let users on older, incompatible hardware continue to use AI masking (*), and it will greatly accelerate troubleshooting when users have incompatible GPUs or out-of-date drivers. In my quickie testing on Windows, these commands take 1-2 seconds with a GPU and 5-10 seconds without (so still quite useable). (+)
Both the CoreML library (Mac) and the ONNX Runtime (Windows) allow the client to specify whether the CPU or the GPU is used to execute models.
Providing the option Use GPU for AI Masking would be exactly in line with the other existing GPU options:
- Use GPU For Display - Use GPU For Image Processing - Use GPU For Export - Use GPU To Apply Dehaze And Clarity Adjustments While Generating Previews
(+) It's easy to demonstrate that AI masking runs correctly but more slowly without a GPU. On an Intel Mac, boot into Safe Mode and run LR -- Activity Monitor demonstrates there is no GPU available. On Windows, run a Parallels Virtual Machine, which won't use the GPU of the host computer.