Does iPhone Duo run iPad apps? The Duo and the iPad mini

Open, iPhone Duo has a 7.6-inch display. The iPad mini’s is 8.3 inches. So the question comes up in every comment thread about the phone: is the open Duo a small iPad, and can it run iPad apps? The short answer is no, but a lot of apps will look as if it were.

It’s an iPhone

TidBITS put the question directly after the announcement, and answered it: “The answer is no: it runs iOS 27, extensively adapted for the Duo and borrowing Split View multitasking from the iPad.” Apple’s own materials call it an iPhone throughout, and the developer tools agree: an app on the Duo is told it is running on an iPhone even when the phone is open.

That settles which apps you get. The App Store on an iPhone offers apps built for iPhone. An app whose developer only makes an iPad version, the way Procreate’s full painting app is iPad only, doesn’t appear. Its iPhone sibling, Procreate Pocket, does, and Savage Interactive says it plans to support the Duo after testing it.

Why many Duo apps will look like iPad apps

Most popular apps are sold as one app for both iPhone and iPad. On the Duo you get the iPhone version, but the iPhone version can now use the iPad layout. The inner display reports regular width and regular height, the same size classes an iPad does, and Apple’s guidance to developers is plain: “On the inner display, your app should look like a natural extension of its iPad layout.”

Some apps already do it without trying. Brian Gerfort ran the current App Store version of ShutterSnitch in the Duo simulator: the cover shows one photo and a strip of thumbnails, and opened, the app switches to its iPad mini layout with a collections panel. GIFwrapped shows its iPad layout, collections beside the grid, when the phone is half folded. Moshi’s developer tried the app on an iPad mini to stand in for the open Duo.

There is a catch. That only happens once an app is rebuilt with the iOS 27.1 SDK. Until then, it runs in an iPhone-sized window on the inner display, iPad version or not. The compatibility guide explains the three cases, and the compatibility tracker notes for each big-name app whether the App Store lists an iPad version.

What the Duo borrows from iPad

• Split View. Two apps side by side on the open display, the first time an iPhone has done it. It is always half and half, and it is two apps, not iPadOS’s freely sized windows. The Split View guide has the details.
• More than one window. “iPhone Duo is the first iPhone to support multiple instances of your app’s UI,” Blake Crosley writes. An app that can open two windows on iPad can do it on the Duo, but new windows only open on the inner display.
• Apple Pencil. “Later this year, iPhone Duo will support Apple Pencil with USB-C,” Apple says, “allowing users to take notes, sketch, or mark up documents on either display.” That is the USB-C model; Apple hasn’t mentioned Apple Pencil Pro.

iPhone Duo and iPad mini, side by side

The open Duo’s display is landscape and almost exactly the proportions of A4 paper, which is how Blake Crosley read Apple’s screenshot sizes. The iPad mini’s screen is a longer, narrower rectangle. Trevor Kay’s Screen Sizes site lays the Duo’s inner screen over both iPad mini generations if you want to see the difference.

So whether the Duo can replace an iPad mini comes down to the apps you use on the iPad. If they are iPhone-and-iPad apps that get a Duo update, you will get something close. If one of them is iPad only, it won’t be there.

For developers

Apple is direct about the trap: “Don’t treat ‘regular width’ as ‘iPad.’ Code that shows an iPad-only layout when horizontalSizeClass == .regular, or that assumes iPhone is always compact, will now run that layout on iPhone too.” Adapty’s guide puts the other side of it: the Duo is an iPhone, so there is “no iPad code path to revive and no separate target to build.” Lay out by size class and available space, never by device. The design guide and the screen sizes guide have the numbers.