Backward compatibility on iPhone Duo

11 Sep 2026 ⋅ 2 min read ⋅ iOS

Table of Contents

Your existing app can run on iPhone Duo without recompiling. But the SDK you build with determines how much of the display your app can use and how its standard navigation and toolbar buttons are arranged.

There are three cases to consider:

Apps built before the iOS 27 SDK.
Apps built with the iOS 27 SDK.
Apps built with the iOS 27.1 SDK.

Before the iOS 27 SDK

If you haven't rebuilt your app with the iOS 27 SDK, it won't take advantage of the full display.

In the example below, the app keeps a narrow layout, leaving unused black space around it. This is especially noticeable when the device is fully open.

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iOS 27 SDK

Building your app with the iOS 27 SDK lets it use more of the available space. In this example, the app expands across the inner display to the left of the status bar, with enough room to show two columns of content.

Notice that the toolbar buttons still sit at the top. The app doesn't yet adopt iPhone Duo's new vertical bar layout.

An app built with the iOS 27 SDK using more of the iPhone Duo display, showing two columns when fully open while its toolbar buttons remain at the top. — An app built with the iOS 27 SDK. Source: Apple's Prepare your app for iPhone Duo (0:54).

iOS 27.1 SDK

To take advantage of the entire display, build your app with the iOS 27.1 SDK. The app's background now extends to the screen edges, including the area behind the status bar. Standard navigation and toolbar buttons adopt the vertical bar layout.

In the example below, the toolbar buttons move from the top to the right side, below the status indicators.

An app built with the iOS 27.1 SDK extending its background to the edges of the iPhone Duo display, with toolbar buttons arranged vertically beneath the status indicators on the right. — An app built with the iOS 27.1 SDK. Source: Apple's Prepare your app for iPhone Duo (1:07).

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Conclusion

Backward compatibility lets people keep using your existing app on iPhone Duo. Building with the iOS 27 SDK gives it more room, while the iOS 27.1 SDK enables the full display experience and vertical bar layout.

Rebuilding is the first step. Check how your content and controls adapt as the available space changes, so your app makes good use of the extra room.

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