Design
- Layout Editor
- Constraint Layout
- Layout Inspector (Experimental)
- PSD File Support in Vector Asset Studio
Develop
- Firebase Plugin
- Updated Code Analysis & Lint checks
- Enhanced accessibility support
- Improved C++ Support Edit & Debugging
- IntelliJ 2016.1.3 platform update
- Samples Browser
- Improved Font Rendering
Build
- Jack Compiler Improvements
- Java 8 Language Support
- C++ ndk-build or CMake
- Merged Manifest Viewer
- Build cache (Experimental)
- OpenJDK Support
- Instant Run Improvements
Test
- Espresso Test Recorder (Beta)
- APK Analyzer
- GPU Debugger (Beta)
- Virtual Sensors in the Android Emulator
If you've been following along with the latest builds on the canary release channel, it should be possible to use the built-in updater for stepping up to the official stable build; however, it seems that older versions, regardless of channel, will probably necessitate a download of the latest IDE installer. This may be intentional because many older projects were reported to have some hiccups while upgrading to more recent versions of Gradle.
Also be sure to update to the latest version of the SDK. In addition to all of the new APIs released for API 24 (Nougat), there have been quite a few changes to the ConstraintLayout to fix bugs, add new features, and adjust syntax.
Source: Android Developers Blog, Android Studio Project Site