Apple confirms iPhone Duo is the first iPhone supporting multiple app instances, and that apps already supporting it on iPad will support it here.
Enable it
Declare multi-scene support in your Info.plist:
<key>UIApplicationSupportsMultipleScenes</key>
<true/>Two constraints to know:
- New windows can only be created on the inner display. The outer display is reserved.
- Because of that, the ability to open a window comes and goes as the device folds.
Request scenes correctly
Use UIWindowSceneActivation to request a new scene. Apple is explicit that you must handle errors when requesting one, since the request can fail depending on device state. The action hides itself automatically when new windows are not available, so a correctly built UI does not offer an option that cannot work.
Design for it, not just enable it
Multiple scenes are worth it when two instances of your app are genuinely useful side by side — two documents, two conversations, a reference beside a draft. If your app is a single linear flow, enabling multi-scene adds state-restoration complexity for little benefit.
If you do enable it, audit anything that assumes one instance: singletons holding view state, notification handling that presents UI globally, and analytics that assume one session per launch.
How to verify
Open a second window on the inner display, use both, then fold the device closed and open it again. Both scenes should restore with their own state intact, and the new-window affordance should disappear cleanly when unavailable rather than failing on tap.