Build for iPhone Duo with Xcode 27.1, no Mac needed

Why the SDK decides how your app looks on the Duo

On the iPhone Duo’s inner screen, iOS treats your app according to the SDK it was built with:

Built with an SDK older than iOS 27.0, the app runs in compatibility mode: iPhone-sized in the middle of the inner screen, with black on either side.
Built with the iOS 27.0 SDK, iOS resizes it to a wide window, so layouts that adapt to width show up. It isn’t fold-aware, though: it isn’t told where the fold is.
Built with the iOS 27.1 SDK, the app fills the whole inner screen and can lay itself out around the fold.

So to see your own app as Duo owners will, you need a build made with Xcode 27.1. Xcode 27.1 needs macOS 26.6 or later (Apple), and since the 27.1 beta it has run only on an Apple silicon Mac (MacRumors). If your Mac is older, is Intel, or you work on Windows or Linux, that used to be the end of it.

What changed

VibeView’s cloud builds compile iOS and Apple TV apps on VibeView’s Macs. They still use Xcode 26.5 by default, so existing projects build exactly as before. A project can now opt in to Xcode 27.1, a stable release, per platform or per run. Beta releases of Xcode are not offered. You then open it on VibeView’s Duo in your browser, so neither the build nor the device needs a Mac.

Before you switch: iOS apps built with the iOS 27 SDK must use the scene-based app life cycle (UIScene), or they don’t launch on iOS 27. Upgrade your framework and adopt it: Capacitor 8.5 or later then npx cap migrate; Flutter 3.41 or later, which migrates automatically only when AppDelegate isn’t customised; React Native 0.88, where an existing app moves its entry point to a scene delegate; Expo SDK 58, whose prebuild generates it while a hand-managed ios/ folder follows Expo’s migration guide. SwiftUI apps, including the Kotlin Multiplatform template, already use scenes; a UIKit app adds a scene delegate. Xcode 27.1 also needs a minimum deployment target of iOS 15.0 or later. VibeView flags a build that iOS 27 won’t launch, and Cloud Builds has the details. If you already see “UIScene life cycle is required”, fix it for your framework. The default build stays on Xcode 26.5, so nothing changes until you opt in.

Build with Xcode 27.1 and open it on the Duo

You need a VibeView account, the VibeView CLI, 0.51.0 or later for build profiles (npm install -g vibeview, then vibeview login), and a project that already builds in the cloud. If it doesn’t yet, vibeview build --cloud asks for the build command and artifact on first run, and Cloud Builds has ready-made commands for React Native, Expo, Flutter, Capacitor and native projects.

Ask for Xcode 27.1. Add "xcode": "27.1" to the iOS build block in vibeview.json:
```
{
  "platforms": {
    "ios": {
      "build": {
        "xcode": "27.1",
        "profiles": {
          "development": { "command": "...", "artifact": "..." }
        }
      }
    }
  }
}
```
Keep your existing profiles. Set at this level, xcode applies to every profile; a single profile can set its own xcode instead. To try it once without changing the file, skip this and pass the flag in the next step instead.
Run the cloud build.
```
vibeview build --cloud --platform ios
```
or, for this run only, vibeview build --cloud --platform ios --xcode 27.1. The flag wins over the build block, which makes it handy in CI. The build log starts with the Xcode version and the iOS SDK your app was compiled against, and the build’s page in the dashboard shows the Xcode version too, so you can confirm it used 27.1.
Open it on the iPhone Duo. In the dashboard, open Devices, pick your app in the App picker, then pick iPhone Duo (iOS 27.1); it carries a Foldable badge. Click Start session. The Duo starts closed, on its cover screen.
Unfold it. Click Open in the bar under the device, or use the Device tab: pick a posture, or turn on Set by angle and drag to any angle from 0 to 180 degrees. The stream switches to the inner screen, and your app fills it.

The iPhone Duo simulator closed, with the Atlas sample app running on its cover screen. — A Duo session starts closed, on the cover screen. Unfolding hands your app to the inner screen.

If the inner screen still shows your app in a phone-sized window, check the build log’s SDK line: the build may have used the default Xcode. Devices shows a short note on the inner screen when it can tell your build used an older SDK.

Apple TV builds and CI

xcode works the same way in a tvOS build block. It applies to iOS and tvOS only; an Android or Android TV build block that sets it is an error. A version that isn’t available is refused when you start the build, before anything is charged, and the error lists the versions you can pick. A local vibeview build ignores it and uses the Xcode selected on your own Mac.

To build both ways in CI, keep the default in vibeview.json and add --xcode 27.1 in a separate job. Every build’s log names the Xcode and SDK it used, so the two are easy to tell apart.

Test the fold once it fills the screen

With the 27.1 SDK build running, the Duo is worth checking in more than one posture: Closed, Partial and Open, plus exact angles in between, in any rotation. Set the iPhone Duo hinge angle from CLI, CI or an agent folds it from a script or a coding agent. An AI agent made a first-class iPhone Duo app shows the layout work that follows, and the iPhone Duo simulator page covers sharing a session and agent control. If you also have a Mac that runs Xcode 27.1 and the Duo is missing there, see iPhone Duo simulator not showing.

Limits worth knowing

Beta runtime. The Duo on VibeView runs on Apple’s iOS 27.1 beta runtime, and behaviour can change between Apple’s builds.
It is a simulator, not the device. Layout, postures and rotation behave as Apple’s simulator does. Camera, sensors, real hinge feel and performance are not simulated, so keep a pass on hardware before a release.
One SDK per build. A build uses one Xcode. To compare the default and 27.1, run two builds; each appears in your app’s build history.
UIScene is not optional on iOS 27. If your app doesn’t launch after the switch, the scene-based life cycle is the first thing to check; VibeView shows a warning on a build that iOS 27 won’t launch. Switching back is removing the xcode line.

Frequently asked questions

Can I build an app for the iPhone Duo without a Mac?

Yes. Add "xcode": "27.1" to your iOS build block and run vibeview build --cloud from Windows, Linux or any Mac. The build runs on VibeView’s Macs with Xcode 27.1, and you open it on VibeView’s iPhone Duo simulator in your browser.

Which Xcode do VibeView cloud builds use?

Xcode 26.5 unless you ask for another version. Xcode 27.1 is also available, through xcode in the build block or --xcode on the command. Beta releases of Xcode are not offered.

Why does my app look phone-sized on the Duo's inner screen?

It was built with an SDK older than iOS 27.0, so iOS runs it in compatibility mode. Rebuild it with Xcode 27.1 to fill the inner screen and see the fold.

Will switching to Xcode 27.1 break my app?

It can, if the app doesn’t use the scene-based life cycle (UIScene): iOS 27 won’t launch an iOS app built with the iOS 27 SDK without it. Upgrading your framework isn’t enough on its own; the app has to adopt it: Capacitor 8.5 or later and then npx cap migrate; Flutter 3.41 or later, which migrates the app when you build only if its AppDelegate isn’t customised; React Native 0.88, where an existing app moves its entry point to a scene delegate; Expo SDK 58, whose prebuild generates it (a hand-managed ios/ folder follows Expo’s migration guide). SwiftUI apps already use scenes. Xcode 27.1 also needs a minimum deployment target of iOS 15.0. Your default builds stay on Xcode 26.5 until you opt in.