Apple has opened iPhone Duo app submissions to the App Store, giving developers a little over two weeks to prepare their apps before the foldable iPhone reaches customers on October 23.
Existing iPhone apps will still run on the Duo, but there’s a catch. Apps not rebuilt with the iOS 27.1 SDK will appear with black borders instead of expanding across the full 7.6-inch inner display.
Your favorite apps may need an update
Apps built with the newer SDK can dynamically resize when you move between the Duo’s 5.4-inch outer screen and its much larger inner display.
That flexibility is important on a foldable, where opening the phone suddenly gives an app considerably more room to work with.
Older apps will remain usable, but the black borders could make some of them feel awkward on a device whose biggest attraction is that expansive folding screen.
Early buyers may therefore see an uneven app experience at launch. Apps updated for the Duo will take advantage of the full display, while others could keep looking like conventional iPhone apps inside a much larger screen until developers catch up.
Xcode 27.1 is already available, and Apple has published guidelines to help developers prepare their apps before submissions opened.
Apple has been here before
A new Apple screen size has created this problem before. When the original iPad arrived in 2010, iPhone apps could run on the tablet before developers updated them, but they initially appeared inside an iPhone-sized window rather than behaving like native iPad apps.
The Duo has a more graceful fallback, yet the challenge is similar. Hardware can introduce a new screen overnight; thousands of third-party apps take longer to adapt.
That could make the first few weeks particularly revealing for the Duo. The usefulness of its 7.6-inch display will depend partly on how quickly the apps people use every day learn what to do with all that extra space.
Preorders for the iPhone Duo open October 16, followed by its release on October 23.
