Xcode adds iOS 5.1 app development support
The update includes SDKs for OS X Lion and iOS 5.1, a code signing workflow for for signing OS X apps with Developer IDs, an in staller for command line tools, support for launching Instruments and File Merge from the Open Developer Tool menu, bug fixes, and more.
Xcode 4.3.1 is available as a free download from Apple’s Mac App Store. It requires OS X 10.7.3 or newer.