How to use iOS 10.3 devices with Xcode 8.2.1

You can avoid both the update to Xcode 8.3 (which works only with macOS Sierra) and the Dropbox download from a random link on GitHub, as suggested in other answers. To work with iOS 10.3 in Xcode 8.2.1, follow these steps:

• Exit Xcode 8.2.1

• Download Xcode8.3.3.xip from Apple (https://developer.apple.com/services-account/download?path=/Developer_Tools/Xcode_8.3.3/Xcode8.3.3.xip) (requires sign-in)

• Unzip ~/Downloads/Xcode8.3.3.xip (in Finder, double-click)

• Copy folder 10.3.1 (14E8301) from ~/Downloads/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport to /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport (in Finder, right click on Xcode.app and ‘Show Package Contents’)

• Remove ~/Downloads/Xcode8.3.3.xip and ~/Downloads/Xcode.app

• Start Xcode 8.2.1. Done.