Xcode 27.1 beta is out: test your app on iPhone Duo

Apple released Xcode 27.1 beta on 18 September 2026, build 27A9269. It is the release that carries the iOS 27.1 SDK and the iPhone Duo simulator, so for the first time you can run your own app on a simulated iPhone Duo instead of reasoning about it from Tech Talks.

It is a beta, not the final release. You can build, run and test with it today. You cannot ship with it: App Store submissions need the release version of Xcode, and Apple has not given a date for that. Pre-orders open on 16 October and the device goes on sale on 23 October.

Apple published two other things the same day: the written Preparing your app for iPhone Duo guide, and Figma and Sketch design kits in the Apple Design Resources.

What you need before you install it

A Mac on macOS Tahoe 26.6 or later. The release notes make this a hard requirement. Check your CI machines as well as your own — a build agent on an older macOS cannot run this Xcode at all.

Install the beta alongside your release Xcode rather than over it. You will keep shipping your current app with the release version until 27.1 is final.

Xcode 27.1 beta includes Swift 6.4 and the iOS 27.1 SDK, and debugs on devices running iOS 17 or later.

The iPhone Duo simulator runs in Device Hub

Simulators in this Xcode run inside Device Hub, the Xcode window that hosts both simulated devices and physical ones paired with your Mac. Choose an iPhone Duo run destination and Device Hub opens a compact window showing your app in the device’s bezel. Choose Manage Devices… from the run destination menu, or Xcode > Open Developer Tool > Device Hub, to open it without running anything.

Apple’s release notes list three known issues in the iPhone Duo simulator. Two of them decide what you can test this week:

• The first launch can take several minutes. Do not assume it has hung.
• Most app extensions cannot run or be debugged in the iPhone Duo simulator. Widgets, share extensions and the rest will need a real device, which means waiting for hardware. Test your main app now and plan the extensions for later.
• StandBy is unavailable in the iPhone Duo simulator runtime.

If Xcode does not offer an iPhone Duo destination, check Xcode > Settings > Components, where Xcode lists the simulator runtimes it has installed and can download.

Previews can show the other display

One new feature makes the second display cheap to check. The canvas overrides picker in Previews now has a Display group for previewing content on a device’s alternative display. On iPhone Duo that means you can compare a view on the 466-point outer display and the 626-point inner display from the canvas, without launching the simulator at all.

If you ship a Mac Catalyst version

Two known issues affect apps that share code with Mac Catalyst:

• Code that calls iOS 27.1 APIs fails to compile for Mac Catalyst, with “undeclared identifier” and “cannot find” errors. Wrap that code in #if !targetEnvironment(macCatalyst) in Swift, or #if !TARGET_OS_MACCATALYST in Objective-C.
• Targets set to iOS 27.1 show no Mac Catalyst run destination. Add a Mac Catalyst 27.0 minimum deployment target in the target’s settings.

Both come with Apple’s workarounds, so neither should stop you testing the iOS build.

What the written guide makes explicit

Until 18 September, Apple’s iPhone Duo guidance existed mainly as six Tech Talk videos. The written guide confirms most of what we drew from them and states a few things more precisely than the talks did:

• Build with the latest Xcode to use the whole screen. An app built with Xcode 26 or earlier does not extend under the status bar and camera. This is the change that reveals layout bugs, so run your app on the 27.1 SDK before you touch anything else.
• Lay out from your scene, not the screen. Size views relative to their container, calculate from the scene or containing view’s bounds, and adapt to size classes. Apple says outright not to use the device idiom or interface orientation for layout decisions.
• Bars go vertical in two places. On the outer display when the phone is closed, and for some views in the leading or trailing position on the inner display. Sheets on the outer display get vertical bars by default; opt out with toolbarVerticalBehavior(_:) in SwiftUI or preferredVerticalBarBehavior in UIKit.
• An item needs an icon to go vertical. A toolbar item with a title and no icon, or with a custom view, is never presented vertically. Give items both.
• Order still runs from the top. Back or Close first, then prominent actions such as Done, using topBarPinnedTrailing in SwiftUI or pinnedTrailingGroup in UIKit.
• The outer front camera always occludes your view, and the inner one does while it is active. The fold is a division region, active while the phone is partially open and inactive once it is fully open.

Our compatibility checklist turns these into fixes you can work through, and the framework guides cover React Native, Flutter, Unity and Capacitor, which have no iPhone Duo support of their own yet.

What to check first

Apple’s guide suggests a walkthrough. This is the order we would run it in:

1. Build your current app, unchanged, with Xcode 27.1 beta and run it on the iPhone Duo simulator. Do this before fixing anything, so you see the real starting point.
2. Check both displays in every pose. Closed, open and partially folded, then rotate each one. Note any layout that assumes a width or an orientation.
3. Look at every bar. Check whether the system moves your navigation bars, toolbars and tab bars to the side. If it does not, you are probably drawing a custom bar instead of using the one a navigation container provides.
4. Open every sheet and popover with the phone open and folded. These are where awkward positioning usually shows up.
5. Look for controls sitting in the fold. Anything important that lands on the division region needs to move.
6. Leave extensions and StandBy for a real device, since the simulator cannot run them yet.

We keep a running page on Xcode 27.1 and the iPhone Duo simulator that we update as Apple ships further betas and the final release.

If you would rather not do this yourself before 23 October, we test apps on the iPhone Duo simulator and fix what we find — see what an audit costs.