IPhone Duo and the Apps That Have Not Been Rebuilt for a Fold

Apple’s developer page for “iPhone Duo,” published September 9, tells app makers to design for dynamic resizing and adaptive layouts, including sessions such as “Design for iPhone Duo” and guidance to “Leverage multiple displays and scenes on iPhone Duo.” Pre-orders open Friday, October 16, and the phone reaches customers Friday, October 23. But the practical tooling for testing fold behavior isn’t ready yet. Apple’s step-by-step document “Preparing your app for iPhone Duo” is marked “coming later this month,” and Xcode 27.1 beta—needed to build, run, and simulate against iPhone Duo—is not yet available. Xcode 27 entered release candidate status on September 9 but supports iOS 27 generally, not Duo-specific tools. As of now, Apple hasn’t documented how apps that aren’t rebuilt will appear on the two screens, nor the exact API details or target resolutions.