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There are two completely different products called “Duo.” For Apple’s iPhone Duo, build a native iOS app with Xcode 27.1, test its adaptive layouts in Device Hub, and submit it through App Store Connect. Apple’s current developer material explains the device’s changing layouts and distribution timeline, but it does not publish a step-by-step procedure for coding or installing a custom native widget.
Doan Labs’ separate, unofficial Duo is a browser-and-desktop simulator. Its custom apps are TypeScript and React web applications compiled by the simulator’s SDK and CLI, then installed from a simulator catalog. That workflow cannot install an app or widget on Apple’s physical iPhone Duo.
First, identify which “Duo” you are developing for
Before opening an editor, decide whether you mean Apple’s foldable iPhone Duo or Doan Labs’ unrelated simulator. The names describe different platforms, different app artifacts and different installation channels.
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| Question | Apple iPhone Duo | Doan Labs Duo simulator |
|---|---|---|
| What it is | Apple hardware running iOS | An unofficial browser and desktop experiment with two displays and a draggable hinge |
| App technology | Native iOS app built with Apple’s SDKs and Xcode | TypeScript and React web app using the simulator’s SDK, UI kit and CLI |
| Testing tool named in the documentation | Device Hub in Xcode 27.1 | The simulator itself and its build tooling |
| Distribution | App Store Connect | A hosted or curated simulator catalog |
| What gets installed | An iOS app distributed through Apple’s platform | A compiled HTML-based simulator app, not an iOS application |
Apple says iPhone Duo availability begins October 23, 2026. The developer announcement describing preparation and submission is dated October 5, 2026, so labels, requirements and availability should be checked again as those dates approach.
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For Apple’s platform, start with Apple’s preparation and submission announcement and the three-step layout guide. For the simulator, use the Duo documentation; it explicitly says the project is not affiliated with Apple.
Build a native app for Apple’s iPhone Duo
1. Use the current Xcode and SDK combination
Apple recommends recompiling existing apps with Xcode 27.1 and using its new SDK support for iPhone Duo. The same release introduces Device Hub, which lets you visualize an app across the device’s poses and orientations. Treat Xcode 27.1 as the starting point for a new or updated project rather than assuming an older simulator configuration represents the Duo experience.
Apple’s documentation describes a specific progression by SDK:
| Build SDK | Behavior described by Apple | Practical implication |
|---|---|---|
| iOS 26 SDK or earlier | The app runs, but does not adapt to all iPhone Duo layouts. | Do not use an older build as proof that every pose or display arrangement works. |
| iOS 27 SDK | The app resizes to fill most of the inner display. | Review every screen when the available area changes. |
| iOS 27.1 SDK or later | The app uses the full display, with toolbars and tab bars presented vertically below the status bar. | Recheck navigation, toolbar placement and content insets against this presentation. |
Apple’s concise statement is that apps built with the iOS 27.1 SDK or later are optimized for iPhone Duo. That is an SDK-compatibility statement, not a promise that an app needs no design changes.
2. Make every screen respond to available space
The central design requirement is adaptability. iPhone Duo can change the amount and shape of usable space as it folds and unfolds, so a fixed-width or orientation-only layout is fragile.
- Use the current view or window dimensions when deciding how to lay out content.
- Read those dimensions again whenever the available size changes; do not cache one measurement for the entire session.
- Use the available shape and size as the layout signal instead of treating portrait or landscape orientation as a substitute. A pose can produce a new geometry without being a simple orientation change.
- Check content that depends on safe areas, status-bar placement, toolbars and tab bars, especially on iOS 27.1 SDK or later where navigation chrome is presented vertically below the status bar.
- Test text, images, lists, split views and controls at each meaningful size rather than validating only the fully open state.
These recommendations come from Apple’s layout-preparation guide. They are more durable than hard-coding a particular screen measurement because the app reacts to the space the system actually provides.
3. Inspect poses and orientations in Device Hub
Open the project in Xcode 27.1 and use Device Hub to visualize the app across the poses and orientations Apple supports. The purpose is not merely to see whether the app launches. Look for changes in hierarchy, clipping, navigation placement and the amount of content visible after each resize.
- Build the project with the iOS 27 or iOS 27.1 SDK selected for the target, depending on the behavior you need to validate.
- Launch the build in Device Hub.
- Move through the available poses and orientations, including transitions between folded and unfolded states.
- At each state, verify that the window dimensions are being re-read and that the layout reflows rather than preserving a stale frame.
- Exercise navigation and data-entry paths, not just the landing screen. A toolbar or tab bar that looks correct in one pose can overlap content in another.
- Repeat the pass after changing constraints or size-class decisions; responsive bugs often appear only after a transition, not at the initial launch.
Apple’s announcement names Device Hub as the visualization tool, but the cited material does not define a separate checklist of required poses. Use the available states in the tool and keep your own regression list for screens that have special geometry.
4. Prepare the release and submit it
When the app has been adapted and checked, Apple’s route is App Store Connect. Apple says optimized apps and games can be submitted there today, relative to its October 5, 2026 announcement.
- Archive the updated app from the Xcode project using the intended iPhone Duo-compatible SDK configuration.
- Upload the build through the normal App Store Connect submission flow for the app.
- Complete the store metadata and review information required for the release.
- Beginning in April 2027, include iPhone Duo screenshots with submissions, because Apple says those screenshots will then be required.
The April 2027 screenshot requirement is date-sensitive. A submission made before that month and one made from April 2027 onward should not be assumed to have identical asset requirements; check the current App Store Connect interface and Apple’s announcement when you submit.
How native apps are installed—and what the sources do not establish
For Apple’s physical device, App Store Connect is the documented distribution route in the cited materials. The sources explain how to prepare an optimized build and submit it, but they do not provide a special “Duo installer,” a custom catalog, or a separate sideload command. Do not treat the simulator’s catalog process as a method for putting an iOS app on iPhone Duo.
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The preparation guide also does not state that you must own the physical phone before beginning development. You can prepare the project with Apple’s development tools and documentation; device ownership, testing access and any account requirements should be confirmed against Apple’s current developer and App Store Connect terms for your release situation.
Custom widgets on Apple’s iPhone Duo: what is documented
Today View on the open device
Apple describes the open iPhone Duo experience as having two Home Screen pages and a vertically scrolling, customizable widget list in Today View. This establishes where users encounter widgets and that the list can be customized, but it does not by itself explain how a developer writes a new widget.
StandBy as a widget hub
Apple also describes StandBy as a hub for widgets with additional face customization. StandBy is therefore another product surface to account for when thinking about the user experience, but the cited announcement does not provide an implementation tutorial, extension template or installation sequence for a custom widget.
The important limit
The Apple materials reviewed for this guide do not establish a step-by-step native custom-widget build and install procedure. They cover the product-level widget experience and the app-layout and submission path. The simulator documentation’s widget API is unrelated and must not be copied into an iOS widget project. If you need the exact native widget-extension APIs, entitlements, target setup or installation commands, consult the current Apple developer documentation for those technologies rather than inferring them from the Duo simulator.
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The Doan Labs project documents a separate workflow for developers who want to make an app that runs inside its browser and desktop simulator. It is useful for experimenting with a two-display interface, but it is not an Apple development or distribution channel.
1. Create the simulator app with its web stack
Write the app in TypeScript and React. The project describes StyleX for styling and provides a UI kit. Its SDK exposes features for display state, fold state, storage, commands, widgets and links. Those APIs model the simulator’s environment; they do not become iOS APIs when the app is built.
2. Build with the project’s CLI
Use the simulator’s CLI and SDK to compile the web app. The documented output includes:
- A release manifest.
- A single HTML document containing the compiled app.
- An app icon.
The single-document output is a simulator artifact. It should not be renamed or submitted to App Store Connect as though it were a native iOS archive.
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The simulator installs apps from a catalog. The documentation allows developers to host their own catalog or submit an app to the project’s curated catalog. Choose the route that matches who needs access:
- Hosted catalog: useful when a team controls distribution for its own simulator instances.
- Curated catalog: appropriate when you want the project to consider the app for its public catalog.
4. Install from the simulator
- Publish the generated manifest, HTML document and icon through the catalog route you selected.
- Open the catalog in the browser or desktop Duo simulator.
- Select the app and use the simulator’s catalog installation action.
- Launch the installed web app and test display, hinge, storage, command, widget and link behavior exposed by the SDK.
The documentation does not turn this into a physical-device installation process. A catalog-installed simulator app remains inside Doan Labs’ environment and cannot be transferred to Apple’s iPhone Duo.
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Native iOS versus simulator: choose the correct workflow
| Decision point | Choose native iOS when… | Choose the simulator workflow when… |
|---|---|---|
| Target user | Your users will run the app on Apple hardware and iOS. | Your users will run an experiment in the browser or desktop Duo simulator. |
| Language and tools | You are working in Xcode with Apple’s iOS SDKs; Apple recommends Xcode 27.1 for Duo preparation. | You want TypeScript, React, StyleX, the simulator UI kit and its CLI. |
| Layout problem | You need to respond to changing iPhone Duo dimensions, poses and orientations. | You want to model two displays and a draggable hinge using the simulator SDK. |
| Widget expectation | You are designing for Apple’s Today View or StandBy surfaces, but need Apple’s widget documentation for implementation details not supplied here. | You are using the simulator’s own widget feature as part of a web app. |
| Release channel | Submit through App Store Connect; iPhone Duo screenshots are required for submissions beginning April 2027. | Install from a self-hosted or curated simulator catalog. |
Common mistakes and how to avoid them
Calling the simulator an Apple SDK
The two projects share a name but not an API, runtime or distribution system. Label internal documentation, repositories and build scripts with the full product name so a simulator catalog command is not mistaken for an App Store Connect step.
Testing only one screen shape
An app that looks correct while fully open can fail after a fold or resize. Use Device Hub for native work and exercise transitions in the simulator for web work. Recheck dimensions after every change.
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Apple specifically recommends using view or window dimensions and re-reading them when they change. Orientation alone does not describe every available shape on a device that folds.
Assuming an older SDK is Duo-optimized
Apple says iOS 26 SDK builds run but do not adapt to all layouts. Move the target to the appropriate iOS 27 SDK level and verify the resulting navigation and content presentation.
Inventing a native widget installation path
The cited Apple sources describe Today View and StandBy but do not supply the implementation procedure. Do not use the simulator’s widget API as a substitute. Find the current Apple widget-extension guidance for the exact target, entitlements and installation method you need.
Forgetting the screenshot date
Apple’s stated requirement begins in April 2027. Keep the submission checklist date-aware so an otherwise valid release is not missing the required iPhone Duo screenshots after that change.
A practical release checklist
- Confirm that the target is Apple’s iPhone Duo or the separate Doan Labs simulator.
- For native work, use Xcode 27.1 and the iOS 27 or 27.1 SDK path appropriate to the behavior you are validating.
- Replace fixed-size assumptions with current view or window dimensions.
- Re-read dimensions after fold, unfold and other size changes.
- Inspect poses and orientations in Device Hub.
- Review vertical toolbar and tab-bar presentation below the status bar for iOS 27.1 SDK or later builds.
- Submit the optimized native build through App Store Connect.
- Add iPhone Duo screenshots to submissions beginning April 2027.
- For simulator work, compile the TypeScript/React app with the project CLI and verify the manifest, HTML document and icon.
- Publish the simulator artifacts to a self-hosted or curated catalog, then install from that catalog.
- Never describe the simulator catalog as a way to install an app on Apple hardware.
Bottom line
Building for Apple’s iPhone Duo means adapting a native iOS app to changing dimensions, checking it in Xcode 27.1 Device Hub and submitting it through App Store Connect. Apple’s published Duo material does not yet provide a native custom-widget coding or installation tutorial; it only documents the Today View and StandBy widget surfaces. The Doan Labs Duo offers a fully documented TypeScript/React catalog workflow, but it is an unofficial simulator with different APIs and artifacts. Select the platform first, then follow only that platform’s tools and distribution path.
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