Is it possible to block Apple Intelligence from sending data over the Internet via Little Snitch? I would assume it is, but I'm not sure if anything significant has changed in macOS 27 that makes this impossible now. I don't really mind the local features - I'd rather they stay disabled, but it's not the end of the world - but I really don't want any data leaving my Mac.
Apple OS will bypass any user space firewall.
You can verify this yourself. Get an old laptop to act as a wifi hotspot and forward traffic over usb ethernet adapter to your actual router. Then run tcpdump on the computer. You will see the multitude of phone-home traffic.
Is it possible to block Apple Intelligence from sending data over the Internet via Little Snitch?
Short answer: Maybe, but I've never tried it.
Little Snitch is aware of various system-level network connections, but I don't know if they're granular enough to block the AI only.