Private frameworks in iOS 27 and macOS 27 let a third-party model stand in for Siri's planner

Sources: MacRumors report, HN discussion
Summary: MacRumors reports two distinct mechanisms found in iOS 27 and macOS Golden Gate 27 private frameworks by a developer posting as pdfu. Model Delegation makes a third-party model appear as a Siri extension that hands a task back to Siri when it needs a system feature, while an inference provider in Model Manager Services replaces Apple's own server-side Siri model and receives Apple's Siri planner prompt and tool definitions, so the substitute can request system actions, receive the resulting personal data and answer through Siri's interface and voice. Neither is usable now, because the "Ask..." menu in the macOS 27 release candidate is limited to the existing ChatGPT extension and Apple has not opened the model delegation entitlement to third parties.
Why it matters: MacRumors notes the EU Digital Markets Act requires Apple to give third parties effective access to features available to its own services, and that the European Commission has said this extends to Siri.
Follow-up: Whether Apple opens the model delegation entitlement to third parties, and whether the inference-provider path appears in a shipping release rather than only in framework code.