Migrating an existing iPhone app to iPhone Duo without a rewrite

Start with what is actually broken

Before reaching for iPhone Duo-specific APIs, the guidance we have seen prioritizes a more basic fix: adaptive layouts over device-specific logic. Concretely, that means auditing your app for two patterns:

• Branching layout logic on device idiom or orientation, rather than on size classes
• Referencing UIScreen.main directly, rather than querying the actual window scene's available geometry

Both patterns predate iPhone Duo by years and were already fragile on any device with variable screen space — Split View on iPad being the most obvious precedent. If your app already avoids both, you are much closer to correct iPhone Duo behavior than a from-scratch rewrite would suggest.

Reach for system containers before custom layout

Standard components like NavigationSplitView in SwiftUI and UITabBarController in UIKit handle fold avoidance and vertical bar adaptation automatically, according to what we have seen documented. If your interface is built from these already, adopting iPhone Duo support may be closer to a recompile against the iOS 27.1 SDK than a redesign. If it is built from fully custom containers, that is the part of the migration actually worth budgeting real time for — and where ArrangementView, covered in our adaptive layouts guide, becomes relevant.

Use the modernization tools in Xcode 27.1

Xcode 27.1 beta includes modernization tools specifically aimed at migrating existing apps to these adaptive patterns. We cover the rest of what is new in that beta, along with the macOS Tahoe 26.6 point release most teams should be running their build infrastructure on, in our developer stack overview.

Test accessibility while you are in there

Since you are already touching layout code, it is a good moment to also verify VoiceOver, Dynamic Type, and contrast across every device pose rather than treating that as a separate pass later — see our accessibility guide for exactly what to check.

What to skip for a first pass

Camera continuity APIs like Virtual Front Camera, multiple-window support through UIWindowSceneActivation, and on-device AI through the Foundation Models framework are all real capabilities worth exploring, but none of them are required to get an existing app looking correct on iPhone Duo. Treat basic adaptive layout as the migration, and treat those as optional follow-up features once the fundamentals are solid.