The iPhone Duo is the first iPhone that can run two apps on screen at once, and it can remember your favorite combinations as pairs.
Unfold the phone in landscape orientation and Split View (two apps sharing the screen) opens on the 7.6-inch inner display. There are two ways in. From an open app, swipe up from the bottom, pause in the center, then drag the app to the left or right edge. The Home Screen fills the other half, and you pick the second app by tapping its icon, using swipe-down search, or swiping left to the App Library. Alternatively, touch and hold an icon, tap Open in Split View, and choose the second app. To swap sides, repeat the swipe-and-drag on either app.
The authors of a published how-to guide for the phone also said they found that two windows of the same app work in certain cases. They named Safari, Mail, Notes and Files as apps that support multiple windows. Tap the app's icon again while it sits in Split View and a second window opens beside it.
To make a pair, tap the divider between the two apps. After that, opening either app launches the other with it. Drag the divider to the left or right edge to unpair: the app you push off closes, and the other returns to full screen.
The limits are specific. Unlike iPadOS, the split is fixed at 50/50, so you cannot give one app more room. Only one app can play audio at a time.
The guide describes all this as the way Split View currently works, and that wording is the authors' own. The guide does not quote Apple or mention planned changes. Our inference, not a finding: a fixed split and single-audio rule read more like a first-version baseline than a settled design, since iPad users already have a resizable divider. Android foldables have offered split screen and saved app pairs for years, so the Duo is arriving at a familiar idea with fewer controls.
Whether 50/50 is a deliberate choice for a 7.6-inch screen or a placeholder is the open question.