The privacy-first app category is heavy on on-device ML and lean on backend. That changes the Flutter-vs-Swift calculus.
Where Flutter wins
Cross-platform reach. Faster iteration. Large ecosystem. For apps that need Android + iOS and don't lean hard on platform-specific ML, Flutter is the pragmatic choice.
Where Swift wins
Native access to Core ML and MLX. Tighter integration with iOS privacy primitives (Secure Enclave, Keychain, App Attestation). If the app's competitive edge is on-device ML, Swift's access to the Neural Engine is material.
The hybrid pattern
Flutter for UI and business logic. Swift for Core ML / MLX integration via platform channels. This is Sovereign's architecture.
The cost of Flutter on iOS
Larger app size (+10-20MB baseline). Platform UI drift on Apple updates. Some flutter packages are thin wrappers with poor Swift interop. Budget two weeks of platform-specific polish that a native app wouldn't need.
When to start with Swift
If you're iOS-only and ML-heavy, Swift. If you need Android, Flutter. For indie developers with limited time, the cross-platform leverage Flutter provides usually wins.
About Sovereign — A privacy-first AI personal assistant that runs entirely on your iPhone. On-device LLM, zero-knowledge encryption, and a coach that learns from your own words. See how it works or visit the homepage.