At Google I/O, the latest version of the Android platform, Android 4.1 (Jelly Bean), was announced. With Jelly Bean, we’ve made the great things about Android even better with improved system performance and enhanced user features.
Android 4.1 is the fastest and smoothest version of Android yet. Google have made improvements throughout the platform and added great new features for users and developers. This document, Android 4.1 for Developers, provides a glimpse of what's new for developers.
See the Android 4.1 APIs document for a detailed look at the new developer APIs.
Source: Android Developers Blog - Introducing Android 4.1 (Jelly Bean) preview platform, and more