Google sold Apple the ability to run certain Gemini models on Apple's data-center hardware, using Google's orchestration layer. Apple hooks into that not dissimilar from an API-provider, and then builds everything upstream.

Meaning the system prompt(s), harness, entry and exit points, and skills. So the product is still "Siri AI", because of all the stuff that takes it from a raw infrastructure concern upon up into a "product" is Apple's responsibility.

Google are "okay with that" because Apple pays them $1B a year, per press reports, to be.

Any business can do this now actually - you just need to lease/rent hardware through a Google partner and you can run an Nvidia based server in your own datacenter running (supposedly) the latest full Gemini models.