Apple's new Siri architecture in iOS 27 and macOS Golden Gate has been designed to swap out AI models entirely, not just add them as side options. A code researcher found two separate mechanisms for this. The first, called Model Delegation, lets third-party AI like Claude appear as a Siri extension alongside the existing ChatGPT option. When you ask Siri to use Claude for something like setting a reminder, Claude handles the natural language interpretation, then hands the task back to Siri to actually execute it in Apple's system. For tasks Claude can't do—like generating a CSV file—it still returns the result to the user. This creates a hybrid where the third-party model does the thinking and Siri does the doing. The second mechanism goes much deeper. Something called Model Manager Services lets Apple replace its own server-side Siri entirely with a different model, like GPT-5.6. In this setup, the third-party model gets Apple's native Siri prompts and tool definitions, meaning it can directly request system actions, access your personal data, and formulate answers that Siri then presents using Apple's interface and voice. The demo shows ChatGPT finding emails about a topic, summarizing them, identifying action items, and sending a message through the Messages app—all while the request gets logged in OpenAI's systems. The EU's Digital Markets Act likely pushed Apple toward this. The regulation requires Apple to give third parties real access to iOS features available to Apple's own services, and the European Commission explicitly said this applies to Siri. Right now, the "Ask..." menu for switching models only works with ChatGPT on macOS, and Apple hasn't opened the model delegation entitlement to other companies yet. But the engineering here shows Apple has built Siri from the ground up to be swappable, not just extensible.