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Announced 9 September 2026

Your iOS app on iPhone Duo: what breaks, and how to fix it

The inner display is 626 × 890 points at an aspect ratio of 1.42 — against 2.17 on iPhone 18 Pro. Layout code that was correct on every previous iPhone is not correct here.

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iPhone Duo display proportions compared with iPhone 18 ProThree screens drawn to the same scale. iPhone 18 Pro is 402 by 874 points, a ratio of 2.17. The iPhone Duo inner display is 626 by 890 points, a ratio of 1.42 — wider and much squarer. The outer display is 466 by 678 points.402 × 874 ptiPhone 18 Profor comparison2.17626 × 890 ptiPhone Duoinner, unfolded1.42466 × 678 ptiPhone Duoouter, closed1.45
Drawn to the same scale. The inner display is not simply larger — at 1.42 it is a different shape from the 2.17 every previous iPhone layout was built for.

First, the good news

Your app will not crash. Apple defined three tiers of behaviour, and the one you get depends entirely on the SDK you build against.

Built againstInner display behaviour
Not the iOS 27 SDKFamiliar size and aspect ratio. Works, but does not use the display.
iOS 27 SDKExtends left of the status bar area on the inner display.
iOS 27.1 SDKReaches the screen edge. Bar buttons lay out vertically under the status bar.

So this is a competitive problem, not a support ticket. The risk is looking dated beside an app that fills a 7.6-inch display — and the trap is that rebuilding against 27.1 without doing the layout work behind it can look worse than not rebuilding at all.

The four assumptions that break

A handful of blockers cause almost everything users actually see. These four account for most of it.

  1. “The screen is about 400 points wide”

    The inner display is 626. Fixed frame widths are off by more than 200 points.

    How to fix it — The screen is about 400 points wide

  2. “Portrait lock means portrait”

    The inner display does not honor supported interface orientations. Your lock is ignored.

    How to fix it — Portrait lock means portrait

  3. “Left and right insets match”

    Safe areas are asymmetric now. Doubling one side puts your content off-centre.

    How to fix it — Left and right insets match

  4. “Phone idiom means small screen”

    iPhone Duo reports the phone idiom with a regular-width display. Your iPad layout never appears.

    How to fix it — Phone idiom means small screen

Pick your stack

Apple ships adaptive APIs for SwiftUI and UIKit. Every cross-platform framework is, so far, on its own.

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