Developer pdfu says a custom macOS 27 extension replaces Siri AI’s server-side planning model with GPT-5.6 Terra while keeping Siri’s interface and voice. According to their write-up, the model receives Apple’s native planning instructions and 20 tool definitions. It can request system actions, receive results containing personal data, and answer through Siri, including interactive elements. The setup uses private Apple interfaces. Pdfu says developing it requires disabling macOS security protections known as SIP and AMFI. Whether Apple will make this available to app developers remains unresolved. The developer also reported compatibility problems: GPT-5.6 returned tool parameters that Siri rejected. Pdfu says they added a filter to remove empty optional parameters to make it work.