iPhone Duo questions, answered

14 questions about building for iPhone Duo, each with its own page. Every answer traces to Apple’s developer material and carries a last-verified date.

• When does iPhone Duo ship, and which iOS version does it run?

  Pre-orders 16 October, on sale 23 October 2026 in more than 70 countries. It ships running iOS 27.1 — the SDK tier at which apps reach the screen edge.

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• Will my existing iOS app break on iPhone Duo?

  No. Apps built without the iOS 27 SDK run at a familiar size and aspect ratio. The risk is looking dated beside apps that fill the 7.6-inch display, not breaking.

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• Is the folding iPhone the same as iPhone Duo?

  Yes. iPhone Duo is Apple's official name. Folding iPhone, foldable iPhone, Apple fold, iPhone flip and iPhone 18 Fold all describe the same device, announced 9 September 2026.

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• What are the iPhone Duo screen dimensions in points?

  The inner display is 1878 × 2670 pixels — 626 × 890 points at @3x, a ratio of 1.42. The outer is 1398 × 2034 pixels, or 466 × 678 points. Point figures are derived, not published by Apple.

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• Why does my app look stretched or cut off on iPhone Duo?

  Because the inner display is 1.42 where an iPhone 18 Pro is 2.17 — a different shape, not a bigger screen. Layout written for the older proportions crops, letterboxes or clips.

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• What is the minimum work to make my app look right on iPhone Duo?

  Remove hard-coded widths, stop relying on orientation locks, handle safe-area insets as asymmetric, and drop idiom-based layout branches. None of those need the new adaptive APIs.

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• Can iPhone Duo run iPad apps?

  No — iPhone Duo runs iPhone apps. But the inner display reports regular width in both dimensions, so the iPad layout already in your codebase is frequently the correct layout to serve there.

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• Do React Native and Flutter support iPhone Duo?

  Neither vendor has shipped iPhone Duo support or guidance. Both frameworks lay out correctly because their layout systems adapt, but reserved regions and arrangements need a native module or platform channel.

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• Which version of Xcode do I need for iPhone Duo?

  Xcode 27.1 or later. It carries the iPhone Duo simulator, the iOS 27.1 SDK and the App Resizability skill. Apple released the beta on 18 September 2026; the final release has no date yet.

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• How do I test my app on iPhone Duo without the device?

  Xcode 27.1 beta, out since 18 September 2026, runs an iPhone Duo simulator in Device Hub. Snapshot tests at 626 × 890 and 466 × 678 points add cheap regression coverage in CI.

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• Do I need to keep content away from the fold?

  Yes, while partly folded. ReservedRegion with kind .division reports where the hinge falls — it is active only when folded and has zero width when flat, so layout must handle it appearing and disappearing.

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• Do I need iPhone Duo App Store screenshots?

  Not yet. Apple lists iPhone Duo screenshot sizes — 1398 × 2034 pixels for the outer display and 2007 × 2853 for the inner — sets no requirement for them, and says uploading them in App Store Connect will be available later this year.

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• How long does iPhone Duo support take to implement?

  Days for an app that already has an iPad layout; one to two weeks for an iPhone-only app with fixed layouts; longer for games and custom-drawn surfaces.

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• Does iPhone Duo use Face ID or Touch ID?

  We have seen third-party reports of Touch ID rather than Face ID, but cannot confirm it from Apple's own developer material. Read LAContext.biometryType at runtime rather than assuming either.

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