Anyway it seems like a small subset of Siri queries utilize ChatGPT, the vast majority of functionality is performed either locally or with Apple's cloud apparently.

They were also pretty explicit about planning to support other backend AI providers in the future.

I believe they will just provide an interface in the future to plugin as a Backend AI provider to trusted parties (like the search engine) but will slowly build their own ChatGPT for more and more stuff.

Also, it seems that most of Siri's improved features will still work without it (though perhaps less well in same cases) -- and therefore Apple is not fully dependent on it.

That’s the only case I can think of where it’s an external tech you’re making requests to, usually it’s things like Rosetta made out of Apple IIRC but integrated internally