They use the GPU but an Apple Silicon GPU has the same high speed access to all the RAM on the machine as the CPU does, rather than having its own walled-off maybe 16 GB VRAM in mainstream gaming GPUs or 24 GB in RTX 4090 or RTX 5090 (MSRP $1999 but in practice $3000-$4000 at the moment). Nvidia A100 (80GB VRAM) apparently cost $15,000 or so.

Not only does Apple's unified memory give the GPU more RAM to use, but it also eliminates copying things between CPU RAM and GPU RAM.

A Mac Mini with 48 GB RAM costs $1799. A Mac Studio with 96 GB RAM is $3999 — until March you could get a Mac Studio with 512 GB RAM for $3999, all of which could be used for your AI model.

https://www.tomshardware.com/tech-industry/apple-pulls-512-m...

Some are coming up used at silly prices.

https://www.trademe.co.nz/a/marketplace/computers/desktops/a...

NB NZ$44,999 is "only" US$25,772.