I agree with their assessment that '"AI mode" is the default' - https://ibb.co/Pz9LqKRb.

That's what I get, in the UK, logged out of Google, from a search in Firefox omnibar using "Google" as provider.

I'm aware that they have other things that can be described as AI modes.

That's AI Overview, just like it says at the top of the box.

AI Mode in that screenshot is the tab to the left of All.