Apple has redesigned iOS 27 to take full advantage of the additional screen space on its first foldable device, the iPhone Duo, rather than simply porting the standard iPhone interface across. Rather than building an entirely new system, Apple has adapted multitasking concepts from iPadOS, which shares its foundations with iOS, stating that the Duo was designed to feel "as natural and intuitive as iPad." This matters because it signals how Apple intends foldables to fit into its ecosystem, treating the device as a hybrid between an iPhone and an iPad rather than just a larger phone.

Key changes include moving standard iOS controls to the side of the screen for easier thumb access when the phone is unfolded, and reworking app layouts to suit the interior display's larger size and the external screen's wider aspect ratio. The iPhone Duo will also be the first iPhone to support the Apple Pencil, usable on both the inner and outer screens, though USB-C Pencil support may not arrive until later in the year according to Apple. iOS 27 has also been adapted for the phone's various physical configurations, shifting on-screen content away from the crease when held partially open like a book, and enabling video playback on the outer screen when the device is propped up like a tent.