Running multiple windows on iPhone Duo with UIWindowSceneActivation

Why the restriction exists

The outer display is a 5.4-inch screen designed for quick, single-task interactions when the phone is folded shut. The inner display, at 7.6 inches and with Split View support, is where iPhone Duo's multitasking model actually lives. Restricting multiple-window activation to the inner display keeps the outer display's interaction model simple and consistent — you are not going to accidentally end up with two overlapping windows on a screen that is not designed to manage them.

What this means in practice

If your app supports multiple windows on iPad today through UIWindowSceneActivation, that same code path should carry over to iPhone Duo's inner display without much additional work. The behavior to test specifically is what happens if a user tries to trigger a new-window action while the app is running on the outer display, or while the device is folded — your app should either defer that action until the inner display is available, or handle it gracefully rather than assuming a new window can always appear immediately.

How this interacts with Split View

Multiple windows and Split View are related but distinct: Split View divides the inner display between two different apps, while multiple-window support lets a single app manage more than one window of its own. A well-behaved iPhone Duo app might use Split View to sit alongside another app entirely, or use multiple windows to, for example, keep a document and its reference material open in the same app at once. For the mechanics of how Split View itself behaves — including why some apps do not fill their half of it correctly — see our explainer on black bars in Split View.

As with most iPhone Duo-specific behavior, the underlying guidance from Apple is consistent: build on system-provided patterns like ArrangementView and UIWindowSceneActivation rather than device-specific branching, and the platform tends to reward that with correct behavior across displays and future hardware generations. See our adaptive layouts guide for the layout half of that same principle.