Craig Hockenberry:

It looks like Xcode 27.1 is needed to test the iPhone Duo resizability - and that hasn’t been uploaded yet.

Jordan Morgan:

Cupertino and Friends™️ dropped six new videos over developing, designing, and crafting great apps for the nascent device:

1. Design for iPhone Duo
2. Prepare your app for iPhone Duo
3. Raise the bar with iPhone Duo
4. Strike a pose with adaptive layouts on iPhone Duo
5. Leverage multiple displays and scenes on iPhone Duo
6. Build a great camera experience for iPhone Duo

Nathan Manceaux-Panot:

In the Duo dev video, they describe how text buttons can’t be moved to the new vertical sidebar, as opposed to icon buttons.

I wonder if that’s one of the reasons Liquid Glass pushed hard for icon buttons, even though these are harder to understand; they make the vertical layout possible at all.

Nico Reese:

Totally confusing to me how the toolbar is ordered completely different between both modes here.

Dennis Oberhoff:

I think the problem with the iPhone Duo for developers is mostly that it does not create any new opportunities in the form of a new market or a new audience.

Previously:

• iPhone Duo
• SwiftUI Toolbars

Update (2026-09-17): See also: Accidental Tech Podcast.

Previously:

• Jumping to 27.2

Update (2026-09-18): Xcode 27.1 Beta (Hacker News) adds support for iPhone Duo, but:

StandBy is unavailable in the iPhone Duo Simulator runtime.

Running and debugging most app extensions is unavailable in the iPhone Duo Simulator runtime.

Update (2026-09-21): Léo Natan:

Apple writing example code in Objective C, in 2026. They are REALLY desperate for developers to support this device.

Natalia Panferova:

On iPhone Duo, navigation controls, toolbar actions, and tabs can move into a shared vertical bar along the edge of the display, leaving more vertical space for content. Apps built with the iOS 27.1 SDK get this adaptation through standard containers such as NavigationStack, NavigationSplitView, and TabView. We continue to declare toolbar actions in their usual placements, and SwiftUI determines how to present them in the current context.

Imthaz Ahamed:

I was going through the iPhone Duo specs and realised the inner screen has a different pixel density to the outer screen. The inner 7.6-inch folding display runs at 1878×2670 and 430 ppi, while the outer 5.4-inch display runs at 1398×2034 and 460 ppi.

Jesper:

The iPhone Duo remains interesting, and is clearly a technical tour-de-force that is the outcome of deep thinking about what a foldable phone can be. But the things that sparkle in my mind when I consider it is just the details. They are very important details that yield a noticeably different product, but they are sprinkles on top of a downward slope in user interface design at Apple that does not care any longer about what users or developers want. All that's important is for this year's device to uproot fundamentals and demand that everyone conform to an arbitrary new intuition.

Update (2026-09-29): Craig Hockenberry:

I don’t remember seeing this mentioned anywhere, but you have to be careful about where you place your safe area constraints.

My first pass moved the constraints on scroll/collection views from the superview leading/trailing to the safe area leading/trailing.

[…]

But if you look at Settings and Safari - our only two examples of “what’s right”, you’ll see the scroll indicators are “outside” the navigation bar and hug the edge of the device bezel.

Design iOS iOS 27 iPhone Duo Liquid Glass Programming Simulator Xcode