iPhone Duo Skills

---
name: iphone-duo-readiness
description: Audit and port an iOS app to iPhone Duo, Apple's first foldable iPhone. Use when asked to support, adapt, prepare, test, or review an app for iPhone Duo, foldable iPhone, the inner/outer display, device poses, or the fold. Entry point that routes to the layout, bars, hinge/scenes, camera, and design skills.
---

# Get an iOS app ready for iPhone Duo

iPhone Duo is Apple's first foldable iPhone: a 5.4-inch outer display and a
7.6-inch inner display sharing one aspect ratio, joined by a hinge the user can
leave at any angle. An existing iPhone app runs on it unchanged — but it will
look like an app that has not been thought about.

This skill is the entry point. Work the checklist, then hand off to the
specialist skill for whatever the app actually does.

## The one idea to hold onto

**iPhone Duo is not a new idiom. It is a wider continuum of sizes.**

Every mistake in this port comes from an app asserting something fixed: this
idiom, this orientation, this screen, this width, this symmetric inset. Every
fix is the same shape — replace the assertion with a question about the space
actually available right now.

If you find yourself writing a branch that means "if iPhone Duo", stop. Write a
branch on size class or available space instead, and it will be right on iPad,
in Split View, under iPhone mirroring, and on whatever ships next.

## Step 1 — Establish the baseline

Find out what the app is building against, because the SDK is the gate:

| Built against | Behavior on iPhone Duo |
|---|---|
| iOS 26 SDK or earlier | Runs, but doesn't adapt. Open, the app sits **centered with empty space around it**. Closed, content shows to the left of the status bar and camera. |
| iOS 27 SDK | Resizes to fill most of the inner display, but still avoids the status bar on the right edge. |
| **iOS 27.1 SDK or later** | Extends to the full display, with toolbars and tab bars vertical below the status bar. Unlocks the reserved-region and arrangement APIs. |

Check the deployment target and the SDK in the project, then say plainly which
tier the app is in. Getting to the 27.1 tier is the single highest-leverage
change; almost everything else in this skill assumes it.

One caution before you ship at the 27.1 tier: that's the point where the bars go
vertical, so confirm the content adapts to that before releasing. Jumping tiers
without checking is how an app ends up with controls overlapping its own layout.