Core IDE changes
- They upgraded the base IDE from IntelliJ 2016.2 to 2017.1.2, which adds a number of new features in 2016.3 and 2017.1 — including parameter hints, semantic highlighting, instant results in search, and much more.
- Many new lint checks.
- Instant Run debug issue 234401 should now be resolved. If a program is paused on breakpoint, app restarting is expected. But if the app is not paused on a breakpoint, it shouldn’t restart and hot swap should work when you only make a method implementation change.
Android Studio 3.0 includes support for the Kotlin language. You can incorporate Kotlin into your project by converting a Java file to Kotlin (click Code > Convert Java File to Kotlin File) or by creating a new Kotlin-enabled project using the New Project wizard. Learn more about Kotlin and Android.
Android Studio 3.0 introduces built-in support for Java 8 libraries and certain Java 8 language features. Jack is no longer required, and you should first disable Jack to use the improved Java 8 support built into the default toolchain.
Support for Java 8 language features
You must check : Android Studio Shortcut key every developer should know
Android Studio 3.0 allows you to create Instant Apps in your project using two new module types: Instant App modules and Feature modules.
Instant Apps support
Android Studio 3.0 also includes a new refactoring Modularize action and the App Links Assistant to help you implement Instant Apps.
Source: What's new in Android Studio 3.0 Canary 6