Getting Started with iPhone Duo Development

What is iPhone Duo?

iPhone Duo is a foldable iPhone that gives apps significantly more available layout space when opened. Rather than introducing a new device category to design for individually, Apple built Duo support on top of the size class and window scene systems that already power iPad and Split View — meaning most of the work to support Duo well is the same work that makes an app resize correctly anywhere.

Do existing apps work?

In practice this means you can ship on Duo today with zero changes, but you'll want to update your layouts to take advantage of the extra space rather than leaving it letterboxed or blank.

Which SDK should I use?

Build against the iOS 27.1 SDK using Xcode 27.1 beta to get the latest Duo-specific APIs and simulator support. If you need to stay on a stable Xcode release for other reasons, iOS 27 already includes the core adaptive layout behavior.

Install Xcode 27.1

Download Xcode 27.1 beta from the Apple Developer site. See the full Xcode testing guide for simulator setup details.

Open Device Hub

Device Hub is where you add the Duo Simulator and drive pose changes — fold, unfold, and rotate — while your app is running.

Run your existing app

Select the Duo Simulator as your run destination and launch your app exactly as you would on any other simulator. No code changes are required for it to launch.

Check layout

With the app running, resize the simulator window and change poses in Device Hub. Watch for content that doesn't reflow, controls that land under the fold, or text that clips — each is a sign your layout is assuming a fixed screen rather than reading the available space.

Follow the compatibility checklist

Once your app runs and resizes reasonably, work through the full compatibility checklist to catch the less obvious issues — safe area handling, Dynamic Type, and testing every pose.

Frequently asked questions