[Developer: iOS 27 Contains Private Interfaces, Allowing Third-Party Models to Replace Siri Backend] According to a post by developer pdfu on Platform X, iOS 27 and macOS 27 include undisclosed interfaces that enable third-party applications to integrate with the 'Siri Extension' or replace Siri AI's server-side model. He demonstrated this using Claude and GPT-5.6 Terra: the latter, as a server-side model, can process Apple's native prompts and tool definitions, execute system operations, and access personal data. Both rely on private permissions, which Apple has recently tightened.