On-device summaries first
Kestrel Mail is designed to support message and conversation summaries on device. Apple Foundation Models is the default path where available, and an optional enhanced local model pack can become the active path when it is installed and ready.
What still uses the network
Mail sync, authentication, attachment fetches that are not already cached, and model-pack downloads still require network access. Those are normal product operations and are separate from the summarization path itself.
Cache-first behavior matters
Kestrel is being built with cache-first reads, local-first drafts, and durable replay for several remote mutations. That approach is meant to improve responsiveness and reduce the feeling that every interaction depends on a round trip to the server.
Optional enhanced local model packs
Enhanced local summaries depend on a downloadable model pack that lives on the user’s Mac. Installing that pack is a deliberate user action, and maintenance controls are intended to make it clear when the pack is present, downloading, or removed.
The distribution flow for that pack is still evolving, so the exact packaging and setup experience may change before public launch.
Product details may evolve
Kestrel Mail is still in active development. Specific implementation details, requirements, and release packaging can change before public launch, but the direction is to keep private intelligence local whenever the platform and the installed model capabilities allow it.