Apple introduced an app modernization skill in the WWDC26 talk Modernize your UIKit app. In Xcode 27.1 that skill is renamed App Resizability, and it now supports SwiftUI and iPhone Duo. Apple presents it as an efficient way to check that your app follows the adaptive layout best practices from Prepare your app for iPhone Duo.
Use it as a first pass
Xcode 27.1 is in beta as of 18 September 2026, and we have not yet run the skill against a real project, so treat this as expectation rather than experience. Judging by the practices it is meant to check, expect it to help with the mechanical, high-volume work: fixed frame sizes, main-screen references, symmetric safe-area arithmetic, and code that will not resize.
It cannot make design decisions. Whether a screen should become a split view, what belongs on the outer display, which actions deserve .visibilityPriority(.high) — those need judgement about your product.
A sensible order:
- Rebuild against the iOS 27.1 SDK.
- Run App Resizability and review every change it proposes.
- Work the blocker items on this checklist by hand.
- Only then consider the new adaptive APIs — arrangements, reserved regions, scene accessories.
Review its output rather than accepting it
Automated fixes tend to be locally correct and globally bland. Replacing a fixed width with maxWidth: .infinity is right in a stack and wrong in a form field that now spans 626 points. Read each change with the surrounding layout in mind.
How to verify
After running the skill, build and walk the pose matrix. Treat its changes as a starting draft to review, not a completed migration.