Which means Apple would have to give OAI and Anthropic access to Gemini, I mean Siri AI.

No, it's more that those apps needs to be able to make all of the tool calls Siri AI can make, which would allow third-party developers to collect data they shouldn't have access to.

App developers can already access the on-device foundational models through an API, but I don't think many developers want to do that because there are better models.