Developer: iOS 27 contains private APIs allowing third-party models to replace Siri backend

According to developer pdfu on X, iOS 27 and macOS 27 include undocumented APIs that enable third-party applications to integrate with "Siri extensions" or replace the server-side model for Siri AI. The developer demonstrated this using Claude and GPT-5.6 Terra, showing that the latter could receive native Apple prompts and tool definitions to execute system operations and access personal data. Both methods rely on private permissions, which Apple has recently restricted.