iPhone Duo app compatibility, explained
Every App Store app opens on iPhone Duo. What changes is how much of the 7.6-inch inner display it uses — and whether it does anything with the fold. Here is how to read the difference.
Updated · 3 min read
Every App Store app opens on iPhone Duo. What changes from one app to the next is how much of the 7.6-inch inner display it uses, and whether it does anything with the fold at all.
What decides how an app looks
On iPhone Duo, an app’s layout depends mostly on which version of Apple’s software development kit (SDK) the developer last built it with. Apple describes three cases in its iPhone Duo preparation guide for developers:
| Built with | Phone unfolded | Phone folded |
|---|---|---|
| iOS 26 SDK or earlier | Runs in its old phone layout, centred on the inner display with unused space around it | Appears on the outer display beside the status bar and camera |
| iOS 27 SDK | Grows to cover most of the inner display, keeping clear of the status bar along the right edge | Looks normal |
| iOS 27.1 SDK or later | Treated by Apple as optimized: uses the whole display, with toolbars and tab bars moved into a vertical position under the status bar | Looks normal |
Apple also asks developers to stop assuming a fixed screen size or orientation, because folding or unfolding can resize an app while it is open. Apps that skip this work may crop images or place controls awkwardly even after a rebuild.
Our three tiers
The SDK only tells part of the story. An app can fill the screen and still ignore the fold, so every listing in this directory gets one of three tiers:
- Built for Duo — also called Made for iPhone Duo. The app does something specific with the hardware: a different layout folded and unfolded, Split View, the half-open position or the outer display.
- Adapted — rebuilt with the iOS 27 SDK or later, so it resizes to the 7.6-inch inner display instead of showing black borders. With the iOS 27.1 SDK it can use the whole screen.
- Compatible — runs unchanged. It looks normal on the outer display and keeps its phone layout, with black borders, when unfolded.
When other sites or developers talk about apps that are “optimized” or “Made for iPhone Duo”, they usually mean what we call Built for Duo: an app that changes its behaviour when you fold or unfold the phone, rather than one that simply fills the larger display.
How we verify a listing
Every listing records the date it was checked and one of these methods:
- Developer statement — the developer confirmed support, for example in release notes or a public post.
- Apple announcement — Apple named or showed the app on iPhone Duo.
- Simulator — tested in the iPhone Duo simulator in Xcode 27.1.
- On device — tested on an iPhone Duo.
When an app changes, its listing is checked again and the date is updated. If a listing says not yet tested on a device, it relies on the source it links to.
Why there is no official list
The App Store has no iPhone Duo filter or badge, so there is no official way to browse optimized apps. Apple named Netflix, Zoom, Slack and Detail as day-one partners and does not publish a wider list. That gap is the reason this directory exists.