DuoReady

How to Test Your App on iPhone Duo with Xcode 27.1

Install Xcode 27.1 beta on macOS Tahoe 26.6+, add the Duo Simulator, and use Device Hub to test fold, rotation, Split View, and both displays without physical hardware.

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Quick answer

Test your app on iPhone Duo with Xcode 27.1 beta by installing it on macOS Tahoe 26.6+, adding the Duo Simulator, and driving fold, rotation, Split View, and both displays from Device Hub — no physical hardware required. As of the 18 September 2026 beta, StandBy and most App Extensions are not yet supported in the simulator.

Apple released Xcode 27.1 beta on 18 September 2026. It is the toolchain that includes the Duo Simulator; Apple's current recommendation is to test there rather than wait for hardware.

  1. 1Confirm macOS Tahoe 26.6+
  2. 2Install Xcode 27.1 beta
  3. 3Audit with App Resizability skill
  4. 4Create an iphone-duo branch
  5. 5Add Duo Simulator
  6. 6Preview with Display picker
  7. 7Device Hub: fold, rotate, split
  8. 8Fix only real issues

Requirements

Xcode 27.1 beta requires macOS Tahoe 26.6 or later and ships Swift 6.4 plus the iOS 27.1 SDK — that SDK is what exposes the Duo Simulator destination.

  • macOS Tahoe 26.6+
  • Xcode 27.1 beta
  • Swift 6.4
  • iOS 27.1 SDK

Install Xcode 27.1

Download Xcode 27.1 beta from Apple Developer downloads — it is the release that includes the Duo Simulator and the iOS 27.1 SDK.

Get the installer from developer.apple.com/download, then confirm the Duo Simulator appears after install. Read the Xcode 27.1 Release Notes before you treat a first-launch delay or a missing feature as a project bug.

App Resizability skill

Xcode 27.1 includes Apple's App Resizability skill with SwiftUI and iPhone Duo guidance. Do not hunt the skill file yourself — tell the agent to find and read the built-in skill, then audit the current project. Do not rewrite the existing UI just for Duo.

  • Adaptive Layout
  • Size Classes
  • Safe Area
  • UIScreen
  • Orientation
  • Scene Lifecycle
  • iPhone Duo dynamic sizes
  • Asymmetric safe area
  1. 1Install Xcode 27.1 beta
  2. 2Have the agent read the built-in App Resizability skill
  3. 3Audit the existing SwiftUI / UIKit project
  4. 4Create an `iphone-duo` branch
  5. 5Test in the Duo Simulator
  6. 6Fix only real compatibility issues

Agent first, Simulator second

Let the official skill audit adaptive layout, size classes, safe area, UIScreen, orientation, and scene lifecycle before you spend time on a Duo-only layout. Then test in the Simulator and keep only the fixes that actually fail. Copyable prompt: AI coding on Resources.

agent-prompt
I installed Xcode 27.1 beta. It includes the iPhone Duo Simulator
and a new agent skill for iPhone Duo layout adaptation.

Find Xcode's built-in App Resizability skill and read it.
Use its iPhone Duo / SwiftUI guidance to audit this project.

Then create an `iphone-duo` branch and do debug and adaptation
work only on that branch.

Prefer real compatibility issues.
Do not rewrite the existing UI just for iPhone Duo.

To use the same skill outside Xcode, export Apple's bundled skills first:

export
xcrun agent skills export

Duo Simulator

The Duo Simulator is the destination Apple ships in Xcode 27.1 for running your app on iPhone Duo without physical hardware.

Add a Duo Simulator in Device Hub so it appears in the run destination list (Window → Device Hub), then launch on that destination. The first launch may take several minutes — that is documented in the release notes, not a hang. Pose and size-class guidance lives on iPhone Duo Poses.

Previews Display picker

Xcode Previews add a Display picker so you can preview the alternative display without launching the Duo Simulator.

Use that picker while you edit SwiftUI to check the other surface quickly. Device Hub is still the place to drive live fold, rotation, and Split View once the Simulator is running.

Device Hub

Device Hub is where you add the Duo Simulator and drive fold, rotation, Split View, and both displays live — pose changes do not require a relaunch.

  • Add a Duo Simulator so it appears in the run destination list (Window → Device Hub).
  • Step through fold and orientation while the app stays running, and confirm the layout updates immediately. Size-class rules: iPhone Duo Poses.
  • Exercise Split View so Compact and Regular widths both reflow without a relaunch.
  • Show the inner display, the outer display, or both, and check that each window scene sizes independently — do not assume UIScreen.main describes either surface.

Common mistake

Don't size either display from UIScreen.main. Inner and outer surfaces are separate window scenes; the global screen shortcut does not name the one you are drawing into. See UIScreen.main on iPhone Duo.

Known issues

Xcode 27.1 beta's Duo Simulator has documented gaps: first launch can take several minutes, StandBy is unavailable, and most App Extensions cannot be run or debugged there yet.

Last checked September 2026

Apple published these limits in the Xcode 27.1 Release Notes with the 18 September 2026 beta. Recheck those notes before you treat a missing StandBy surface or an extension that will not attach as an app bug. For everything else, run the compatibility checklist.

Frequently asked questions

Do I need physical iPhone Duo hardware to test my app?

No. Apple's current recommendation is to test using the Duo Simulator in Xcode 27.1's Device Hub, which can drive every fold, rotation, and Split View state without physical hardware.

Which Xcode version includes the Duo Simulator?

Xcode 27.1 beta, which ships with the iOS 27.1 SDK. That SDK is required for the Duo Simulator device to appear in the destination list.

What macOS version does Xcode 27.1 require?

macOS Tahoe 26.6 or later. Xcode 27.1 beta will not install on an earlier Tahoe point release.

Why is the first Duo Simulator launch so slow?

Xcode 27.1 release notes say the first Duo Simulator launch may take several minutes. Wait for that boot to finish before treating a blank or stalled window as a failure.

Can I test StandBy or App Extensions in the Duo Simulator?

Not in Xcode 27.1 beta. Release notes report StandBy is unavailable, and most App Extensions cannot be run or debugged there yet. Use the compatibility checklist for the rest of the Duo matrix.

How do I preview the alternative display without running the Simulator?

Use the Display picker in Xcode Previews. It lets you preview the alternative display while editing, without launching the Duo Simulator.

Should I rewrite my UI for iPhone Duo before testing in the Simulator?

No. Have a coding agent find and read Xcode 27.1’s built-in App Resizability skill, audit the existing SwiftUI or UIKit project, create an iphone-duo branch, then test in the Duo Simulator and fix only real compatibility issues. Do not ship a Duo-only UI first.