Preparing your app for iPhone Duo: the short version

If your app is still built against the iOS 26 SDK, it’s letterboxed on iPhone Duo’s inner display. Here’s the shortest path to full screen, based on Apple’s developer sessions.

1. Rebuild with Xcode 27.1

Xcode 27.1 (beta since September 18, 2026) includes the SDK and an iPhone Duo simulator with controls to open, close, rotate and fold the device. Building against iOS 27 removes most of the letterboxing; building against iOS 27.1 lets your app reach the edges and move standard toolbars into vertical arrangements.

2. Let size classes drive your layout

The outer display behaves like other iPhones. The inner display reports a regular size class in both dimensions, like an iPad. If your app already supports iPad, much of the work is done. Replace any orientation checks with size-class logic: the inner display ignores the orientations your app declares, so you can’t lock it to portrait there.

3. Respect reserved regions

The fold and the under-display camera are exposed as reserved regions. Safe-area insets on the inner display can be asymmetric, so handle each edge independently. Keep interactive content inside the safe area and let backgrounds extend past it.

4. Adopt the new containers

ArrangementView gives you split or overlay arrangements of a primary and secondary view. NavigationSplitView and a sidebar-placed TabView adapt automatically.

5. Use the hinge for delight, not layout

SwiftUI’s onHingeChange and UIKit’s UIHingeInteraction report closed, partially open and fully open states plus a continuous angle. Apple recommends using it for interactions and effects, not for layout decisions.

6. Camera apps: the outer display

CameraCaptureAccessory lets a camera app show extra UI on the outer display while the main UI stays inside — for example a preview for the person being photographed. It’s only available while your app is full screen on the inner display with an active camera session, so observe availability changes.

7. Add iPhone Duo screenshots

Apple says the Made for iPhone Duo badge appears on your App Store product page once you submit iPhone Duo screenshots in App Store Connect. Starting in April 2027, every app submission must include them.

8. Tell people

Mention iPhone Duo in your release notes — our daily scan picks it up — and submit your app for a listing and a badge.