For developers · Checked 1 October 2026

Preparing your app for iPhone Duo

Short answer: iPhone Duo is a foldable iPhone with a compact outer display and a large inner display, each with a front camera. Apple’s guidance comes down to three things: make your app resize with size classes and scene geometry instead of fixed iPhone dimensions, let the system present your bars vertically on the side of the display, and keep content clear of reserved regions such as the fold. Apple also says to build with the latest Xcode: apps built with Xcode 26 or earlier don’t extend under the status bar and camera. The SDK is in Xcode 27.1 beta.

What to use on iPhone Duo

From Apple’s «Preparing your app for iPhone Duo» documentation, read 1 October 2026.

Need	SwiftUI	UIKit
Adapt to size changes	horizontalSizeClass, verticalSizeClass	Size class traits with automatic trait tracking, Auto Layout
Know if bars are vertical	toolbarVerticalEdge environment value	verticalBarEdge trait
Keep sheet bars horizontal	toolbarVerticalBehavior(_:)	preferredVerticalBarBehavior
Control bar overflow	visibilityPriority(_:), ToolbarOverflowMenu	visibilityPriority, additionalOverflowItems
Primary and secondary view around the fold	ArrangementView	UIArrangementViewController
Find the fold and camera areas	reservedRegions on GeometryProxy	reservedRegions(kind:options:)
Extend a hero image under a vertical bar	backgroundExtensionEffect()	UIBackgroundExtensionView

Resizing comes first

As iPhone Duo opens, closes, folds and rotates, your app moves between displays and changes size. Apple notes that if your app already resizes on iPad and Mac or in iPhone Mirroring, you are well on your way. Prefer system layouts and containers such as split views, tab bars, arrangement views and navigation stacks, size views relative to their container, and base layout calculations on the scene or containing view’s bounds rather than screen dimensions. Apple says not to use userInterfaceIdiom or UIInterfaceOrientation for layout decisions. The design guidelines add a simple baseline: a compact width layout for the outer display and a regular width layout for the inner display.

Toolbars and tab bars on the side

Because the outer display is wider and shorter than other iPhones, the system puts navigation bars, toolbars and tab bars vertically on the side; on the inner display they stay on the side in some layouts too. You get this automatically only with container-provided bars: in SwiftUI use toolbar(content:) on a NavigationStack or NavigationSplitView, in UIKit set toolbar items on a view controller inside a navigation controller rather than building custom bars. Put Back or Close at the top, followed by prominent actions like Done. Give items both an icon and a title: an item with only a title, or a custom view, is not shown vertically.

The fold and other reserved regions

iOS describes areas your content should avoid as reserved regions: the outer front camera, always present; the inner front camera, only while active; and the folding region, active when the device is partially open. System alerts, menus, sheets and split views adjust automatically; custom views should read the reserved regions and move content out of them. For a two-part screen, an arrangement view places a primary and secondary view side by side, stacked, or split across the fold. In grid layouts Apple suggests an even number of columns so content divides cleanly at the fold.

Camera apps and games

Apps that capture with AVFoundation or AVKit can use the outer, inner and rear cameras, and after the phone opens or rotates the active camera may face the other way, so choose cameras by the direction they face. For games, Apple allows locking to portrait or landscape but asks that the game fill the screen in every pose, preferring a different aspect ratio over letterboxing or pillarboxing.

Testing and resources

Test in the simulator or on a device in every pose: closed, fully open and partially folded, rotating in each. Apple’s iPhone Duo page lists tech talk videos, Group Labs, forum Q&As and in-person workshops, and Figma and Sketch design kits are in Apple Design Resources. The same resizing theme runs through Android: see Android 17 on large screens. For new App Store listing assets, see App Store creative assets.

Where Censuus fits

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Frequently asked questions

What is iPhone Duo?

A foldable iPhone with a compact outer display and a large inner display, each with a front-facing camera, and a center hinge that supports several poses.

Do I need to rebuild my app for iPhone Duo?

Apple recommends building with the latest Xcode. Apps built with Xcode 26 and earlier don’t extend under the status bar and camera on iPhone Duo.

Which Xcode supports iPhone Duo?

Apple points developers to Xcode 27.1 beta for the SDKs to build, run and test apps for iPhone Duo.

What are the iPhone Duo screen sizes?

Apple’s developer documentation and design guidelines for iPhone Duo don’t list fixed sizes; they ask apps to adapt using size classes, compact width on the outer display and regular width on the inner display.

Why are my toolbar items missing on iPhone Duo?

When bars are vertical, items with only a title or a custom view are not shown. Give items both an icon and a title, and use visibilityPriority to control which go to the overflow menu.

Guides for app developers

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