Apple has begun seeding the latest iOS 5 beta to developers – iOS 5.1 and XCode 4.3.
iOS SDK 5.1 provides support for developing iOS applications and includes the complete set of Xcode tools, compilers, and frameworks for creating applications for iOS and Mac OS X. These tools include the Xcode IDE and the Instruments analysis tool among many others.
With this software you can develop applications that run on iPhone, iPad, or iPod touch running iOS 5.1. You can also test your applications using the included iOS Simulator, which supports iOS 5.1. There are two Xcode iOS SDK 5.1 images, one for installing on a Macintosh computer running Mac OS X 10.6.7 (Snow Leopard) or later, the other for installing on a Macintosh computer running Mac OS X 10.7 (Lion).
iOS 5.1 Beta is available for iPhone 4S, iPhone 4, iPhone 3GS, iPad 2, iPad & 3rd and 4th generation iPod touch. Release notes are available at BGR.