Do your apps work on iPhone Duo? What happens before they're updated
Every iPhone app opens on iPhone Duo, but only updated ones fill the inner display. What an app looks like before its developer adapts it, how to tell which are ready, and which popular apps have said so.
If you are about to order an iPhone Duo, the practical question is whether the apps you use every day will work on it. The short answer is yes, all of them. The longer answer is that “works” and “uses the big screen” are different things, and for most apps the second one needs an update that only became possible to ship on October 5.
In short
- Every app on the App Store opens on iPhone Duo. Nothing is locked out.
- Closed, an app that hasn’t been updated looks exactly as it does on any iPhone.
- Open, it does not fill the inner display. How much it gets depends on the tools its developer last built it with.
- Apple’s own apps are adapted. Apple named four others at the announcement: Netflix, Zoom, Slack and Detail.
- Most big-name apps have not announced anything yet. We keep a compatibility tracker for those.
Closed, nothing changes
The outer display is a 5.4-inch iPhone screen, and an app that has never heard of iPhone Duo runs on it like on any other iPhone. This is the pose you will use most, and it is the one where you will notice un-updated apps least. The one visible difference belongs to updated apps: iOS 27 moves their back buttons, tab bars and toolbars into a column down the side of the display, which leaves more of the short screen for content.
Open, it depends on when the app was built
The inner display is 7.6 inches and wider than it is tall. What an app does there comes down to which version of Apple’s developer tools it was last built with. Apple’s engineers laid out three cases for developers in September:
| The app was built with | What you see on the open Duo |
|---|---|
| Last year’s tools (Xcode 26) | The app in an iPhone-shaped window, with black borders around it. |
| The iOS 27 SDK | The app resizes to use more of the display. Some space is still left over. |
| The iOS 27.1 SDK | The app reaches the edges of the display and its bar buttons move to the side. Apple calls this “optimized for iPhone Duo.” |
9to5Mac, which went through the three modes on the day of the announcement, described the first as the default compatibility mode: the app sits in a safe area on a black background. AppleInsider’s headline for the same thing was blunter: “Apps will look terrible unless they are updated for the iPhone Duo.”
It is the same thing that happened when the iPad arrived and iPhone apps ran in a window in the middle of it. It is not broken. It is a phone app on a screen it was not designed for.
Being built with the newest tools is also only the start. An app can fill the screen and still do nothing useful with the width: one long list stretched across 7.6 inches. The apps worth opening the phone for show you more when you do, a list beside its detail or a video above its controls. That is what the labels on FoldHunt’s app pages record.
Why most apps aren’t ready yet
Apple announced iPhone Duo on September 9 and put the tools for building Duo apps into beta on September 18. Apple does not accept App Store submissions built with beta tools, so for nearly a month a developer could run a Duo layout in the simulator and could not release it. The finished tools, Xcode 27.1, arrived on October 5, the same day Apple began accepting apps optimized for iPhone Duo. The phone goes on sale October 23.
So an app updated before October 5 cannot be the fully optimized kind, whatever its developer has planned. Small developers have moved fastest: FoldHunt lists more than a hundred apps whose makers have shown a Duo layout. Large companies run on their own release schedules. AppleInsider’s William Gallagher expects firms such as Microsoft and Adobe to be slow, as they have been with new Apple screens before.
Which apps are ready
- Apple’s apps. “Apple apps are optimized for iPhone Duo,” the company says. That covers Messages, Mail, Photos, Safari, Music, Camera and the rest.
- Apple’s launch partners. Netflix, Zoom, Slack and Detail were named by Apple as already adapted. They are on our launch partners page with what each one changed.
- Apps whose developers say so. The directory lists every app and game whose developer has shown or announced an iPhone Duo version, each with the post or video it comes from. Our picks of the best so far are the ones that do the most with the open phone.
- Everything else. Instagram, WhatsApp, YouTube, TikTok, Spotify, Google Maps and most other household names have not announced a Duo version that we have found. The compatibility tracker has a page for each, with the date we last checked.
How to tell if an app has been updated
The App Store does not label it for you, as far as we have seen. Three things to look for:
- The release notes. A developer who has done the work will usually say so under “What’s New”. Apple’s own phrase is “optimized for iPhone Duo”.
- The screenshots. App Store pages can now carry iPhone Duo screenshots, one size for each display. They are optional for now. From April 2027 Apple requires them for every app or game submitted.
- Our pages. Each app on FoldHunt carries a label that says where the information comes from: Launch partner, Simulator verified, Developer claimed, or Not announced. On any app that is not yet confirmed you can leave an email address and get one message when it is.
What we don’t know yet
Nobody outside Apple and a few press events has used the phone. Until October 23 we cannot tell you how a particular un-updated app looks on real hardware, whether there is a setting to zoom one to fill the screen, or how un-updated apps behave in Split View. Checking on a real iPhone Duo starts on October 23, and the tracker will be updated as it happens.
If you build apps, the developer’s side of this page is the App Store submission guide.
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