A developer testing macOS 27 beta 6 has reverse-engineered the exact plumbing Apple built for third-party AI providers, and it already works well enough to run Claude and inside Siri’s Ask menu and swap Siri’s own model for OpenAI’s GPT-5.6 Terra. The findings, posted to r/MacOSBeta, show Apple’s long-rumored “Siri Extensions” system isn’t a future promise buried in a roadmap. It’s sitting in the current beta, months ahead of any announced launch.
Bloomberg’s Mark Gurman first reported on Apple’s Extensions plan back in March 2026, describing a system where agents from installed apps work with Siri and the Siri app. By May, Gurman reported Apple had signed a deal to bring a Google Gemini-based model into Apple Intelligence for iOS 27, on top of letting users pick third-party chatbots like Claude and Gemini instead of being stuck with ChatGPT. What the Reddit user found is the technical scaffolding for exactly that plan, already functional in a developer build. Here’s how the two discoveries work, step by step.
Getting Claude Into Siri’s Ask Menu
The first discovery shows how a sandboxed third-party extension gets treated as a native AI provider inside Siri, using an internal Model Delegation API tucked inside Apple’s App Intents framework.
- Build the extension against the Model Delegation API: the developer used this internal hook in App Intents to register a third-party provider that macOS discovers automatically as an AI option, the same way ChatGPT is discovered.
- Trigger the request from Siri’s Ask… menu: selecting Claude from the menu fires the same underlying flow that the built-in ChatGPT extension uses, so from the system’s point of view, Claude looks like any other native provider.
- The sandboxed extension forwards the request over localhost: because the extension itself is sandboxed, it can’t talk to Claude directly, so it opens a framed localhost connection to a companion LaunchAgent running outside the sandbox.
- The LaunchAgent calls the Claude CLI: that agent invokes an authenticated
claude -pcommand-line session with streaming JSON output and a tightly scoped set of MCP tools, keeping the model’s capabilities limited to what the extension explicitly allows. - The bridge translates Claude’s output back into Apple’s format: text deltas, generated files, tool calls, and device-action requests all get converted into Apple’s native response objects, including IntentFile objects, Writing Tools output, suggestions, and Siri intent handoffs.
- Compare it against Apple’s own implementation: the developer found Apple ships a full working ChatGPT integration on disk at
/System/Library/ExtensionKit/Extensions/GenerativePartnerPrototypeExtension.appex, which can be inspected to extract the exact prompts, tools, and output schemas Apple uses for its own ChatGPT requests.
The developer summed up the flexibility of the design directly:
“You can theoretically build a bridge from the AgentIntent to any model backend, including CLIs that support local models.”
That flexibility already shows up in practical differences. Siri AI can’t create files on its own, but the Claude extension can return a CSV when asked, and when a request needs to touch the system, like setting a reminder, the extension relays it back to Siri, which handles it natively.
Apple’s rumored Siri Extensions quietly shipped in macOS 27. I got Claude working.
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Swapping Siri’s Model Entirely
A follow-up post from the same user goes further than adding a provider alongside Siri: it shows macOS 27 letting a third-party app replace Siri’s underlying model outright.
- Confirm the swap path exists: instead of routing a separate request to an outside extension, the demo shows Siri’s own responses being generated by OpenAI’s GPT-5.6 Terra model, not Apple’s built-in Siri AI.
- Match it against Apple’s documented Dynamic Profiles: Apple’s own “What’s New in macOS 27” developer notes describe this directly:
“Dynamic Profiles let you swap models, tools, and instructions on the fly, so your app’s behavior can adapt within a continuous session.”
- Tie it to Apple’s Core AI framework: Apple’s documentation frames Core AI as “a new framework built directly into the OS and purpose-built for Apple Silicon, providing the best way to bring your own models on-device, complete with supporting tools and technologies,” which is the same layer this model-swapping runs through.
You can swap Siri’s model in macOS 27. Here’s Siri AI running on GPT-5.6.
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GPT-5.6 Terra is a real, current OpenAI model, not a placeholder. OpenAI launched the GPT-5.6 series in a limited preview in June, with Terra positioned as the balanced everyday work model sitting alongside flagship Sol and the faster, cheaper Luna, similar in performance to GPT-5.5 but at half the price. It went broadly available in ChatGPT and the API on July 9, priced at $2.50 per million input tokens and $15 per million output tokens.
None of this is exposed through any public setting yet. It requires the internal API access this developer found through beta 6. For everyday users, the officially confirmed way to switch providers today is far simpler – the iOS 27 Siri app defaults to Siri AI but lets you long-press the input field, tap “Ask…,” and pick ChatGPT instead, though closing and reopening the app currently reverts you to Siri even mid-conversation, and context never carries over between providers.
Apple hasn’t said when the official Extensions system, or a dedicated App Store section for choosing third-party AI providers, will actually ship. But with this much of the underlying mechanism already functional in a public beta, and a wide release of macOS 27 expected alongside the iPhone 18 Pro this September, the gap between “hidden in the beta” and “available to everyone” looks a lot smaller.
