Preparing your app for iPhone Duo: a developer checklist
What changes for your app on iPhone Duo, which SDK gets you full-screen, and the fold-aware features that earn a Built for Duo listing.
Updated · 2 min read
iPhone Duo pairs a 5.4-inch outer display with a 7.6-inch inner display and ships with iOS 27.1. Your app already runs on it. This checklist covers what it takes to go from runs to fills the screen to built for the fold.
1. Rebuild with the latest SDK
How your app looks on the inner display depends mostly on the SDK you last built with:
- iOS 26 SDK or earlier — your app keeps its phone layout on the inner display, centred with black borders.
- iOS 27 SDK — it grows to cover most of the inner display, keeping clear of the status bar along the right edge.
- iOS 27.1 SDK or later — Apple treats the app as optimized. It uses the whole display, and toolbars and tab bars move into a vertical position under the status bar.
Rebuilding alone moves your app from Compatible to Adapted in our directory.
2. Stop assuming a fixed screen
Folding and unfolding can resize your app while it is open. Apple asks developers to stop assuming a fixed screen size or orientation. In practice:
- respond to size changes instead of reading the screen size once at launch;
- let images and media reflow rather than crop;
- check that controls near the edges still make sense at both sizes;
- keep state (scroll position, selection, playback) across the change.
3. Design for the fold
These are the features that earn a Built for Duo listing:
- A different layout folded and unfolded — a list on the outer display, list and detail side by side when unfolded.
- Split View — work well next to another app on the inner display.
- The half-open position — use the two halves of the inner display for different jobs, such as content on top and controls below.
- The outer display — a glanceable, purpose-built view for when the phone is closed.
4. Tell people — and us
The App Store has no iPhone Duo badge, so people rely on what you say:
- mention iPhone Duo in your release notes, naming what changes;
- upload iPhone Duo screenshots to your App Store listing;
- submit your app to this directory. Listing is free, every submission is reviewed by hand, and a public source (release notes, a blog post, App Store screenshots) gets you listed faster.