Apple has built Siri to work with outside AI models more deeply than previously known. Private code in iOS 27 and macOS Golden Gate shows two mechanisms. One, called Model Delegation, lets Claude appear as a Siri extension alongside the existing ChatGPT one. In a demonstration, Claude read a spoken reminder request and handed the system action back to Siri. Claude also produced a CSV file, which Siri cannot do itself. A second mechanism can replace Apple's own server-side Siri model entirely. In that case GPT-5.6 received Apple's Siri planning prompt and tool definitions. It could trigger system actions, receive personal data and answer through Siri's voice. Apple has not opened the entitlement to third parties, and users cannot see it. The findings come from a developer known as pdfu, who posted videos on X.