iPhone Duo Group Lab | 9/16/26 | Meet with Apple

Summary

Apple engineers and designers answered developer questions about preparing apps for the foldable iPhone Duo. Their central recommendation was to make apps resizable and adaptive across sizes and poses, using system components and layout APIs wherever possible rather than building a separate custom interface for every configuration.

Development tools and timing

• Beta versions of Xcode 27.2 and the 27.2 operating systems were announced as available for testing.
• The panel said iPhone Duo would launch on iOS 27.1. Xcode 27.1, expected later that month, would add Duo development support, including updated SDKs and DeviceHub support for its poses and orientations.
• Figma and Sketch design kits were already available on Apple’s developer website.
• An updated Xcode “modernize your app” skill was expected in Xcode 27.1. It would support SwiftUI as well as UIKit and provide guidance for Duo layouts.

Layout, poses, and system APIs

• Existing adaptive iPhone and iPad layouts are a strong starting point. Apps that already resize well—particularly those using standard navigation, tab, and split-view components—often need relatively little additional work.
• Developers should generally respond to available space and size classes rather than relying only on device orientation. The inner display can resize and change size classes even when an app’s supported orientations are restricted. Apple strongly recommended removing orientation restrictions where possible.
• Apple described a range of fold-related APIs, from reading the hinge angle to using reserved-region information and arrangement views. The best choice depends on the app; higher-level components can handle much of the adaptation and transition behavior.
• Apps do not need to invent a unique experience for every pose. Start with reliable resizing and standard patterns, then add pose-specific behavior where it genuinely benefits the task. Smooth transitions matter when layouts change.

Vertical bar and standard controls

• A UITabBarController or SwiftUI TabView can adapt its tab bar to Duo’s vertical bar automatically. A custom tab bar will not automatically move there; developers may need to adopt lower-level alignment APIs and account for the bar’s changing position and asymmetric safe areas.
• The Maps and Find My teams migrated custom bars and navigation structures to standard system components, enabling support for the vertical bar.
• Standard tab bars also provide system behaviors, such as revealing labels on touch-down—details that are difficult to reproduce with a custom implementation.

Adapting app content

• Maps moves its sheet to the leading edge on the larger display, leaving more of the map visible. It also reframes map content where useful.
• TV displays more detail and content on the larger screen. In a laptop-like pose, its video layout can move controls below the video, with arrangement views helping animate the change.
• Three-column iPad-style interfaces may show two columns at a time on Duo, with other columns available as overlays. The panel recommended SwiftUI’s NavigationSplitView or UIKit’s UISplitViewController for this type of structure.
• Whether tabs and a sheet should stay together depends on how they relate. For example, Find My keeps its tabs with the sheet because the selected tab determines the sheet’s content.
• Apps can support multiple instances, similarly to iPad. Multiple instances of the same app share the app’s state and use existing SwiftUI or UIKit update mechanisms.
• Full-screen apps, including immersive AR apps, remain possible. The vertical bar need not be used when it does not suit the experience.

Compatibility and testing

• Apps built with Xcode 26 were described as appearing letterboxed on Duo. Building with Xcode 27 and supporting resizing uses more of the inner display, while Xcode 27.1 was expected to enable full-screen support.
• Apps that are not yet adapted receive a familiar iPhone-sized presentation on the outer display and a centered, letterboxed presentation on the inner display. They do not adapt to different poses.
• Developers can use iPhone Mirroring’s resizing for preliminary checks. It can reveal layout and resizability problems, but Duo-specific testing is needed for features such as the vertical bar and its asymmetric safe areas.
• Avoid assuming safe areas, content insets, or margins are symmetrical. Use system-provided layout guides and insets.
• The panel said there is no way to disable resizing when linking an app against iOS 27. It nevertheless recommended starting with basic resizability, then improving pose-specific experiences over time.

Camera and accessibility

• Only apps with an active camera session and the relevant system entitlement can show a camera companion display on both inner and outer screens simultaneously.
• The device can be placed in different seated configurations. The panel said the interface should work in either orientation but did not confirm an API for detecting which side is resting on a table.
• Accessibility guidance included supporting Dynamic Type and readable-content guides, testing Reduce Transparency with the vertical bar, and accounting for VoiceOver across both displays.

Guides and resources mentioned

• “Prepare your app for iPhone Duo”: referenced for the Xcode compatibility progression and the updated modernization skill.
• Tech talk videos released the prior week: referenced for iOS 27.1’s Duo-focused features.
• Figma and Sketch design kits: available on Apple’s developer website.

Main speakers and sources

• Kurt — host and technology evangelist on Apple’s Worldwide Developer Relations team.
• Tommy — UI frameworks engineer.
• Nate — Human Interface Design interaction designer.
• Brandon — Human Interface team designer.
• Nina — engineer on the TV app team.
• Emanuel — iOS engineer on the Maps team.