Code analysis reveals Apple has built iOS 27 and macOS Golden Gate with deep support for swapping Siri's AI engine with third-party models like Claude or ChatGPT. The system works at two levels: as extensions that handle specific tasks, and as complete replacements for Apple's server-side Siri model that can access all system features and personal data.

• Model Delegation allows third-party AI (Claude, ChatGPT) to appear as Siri extensions, handling tasks like creating reminders or CSV files while passing system-level requests back to Siri itself.
• A second protocol in Model Manager Services lets developers completely replace Apple's Siri model with alternatives like GPT-5.6, giving those models full access to Apple's native prompts, tool definitions, and system actions.
• The EU's Digital Markets Act likely drove this design, as it requires Apple to grant third parties effective access to iOS hardware and software features available to Apple's own services, including Siri.
• ChatGPT extension is currently live in macOS Golden Gate, but Claude support and broader third-party access aren't yet available to users or developers.