Instant Run is a behavior for the Run and Debug commands that significantly reduces the time between updates to your app.
Introduced in Android Studio 2.0, Instant Run is a behavior for the Run and Debug commands that significantly reduces the time between updates to your app. Instant Run pushes changes to methods and existing app resources without building a new APK, so code changes are visible almost instantly.
Instant Run is supported only while deploying a debug build variant, using Android Plugin for Gradle version 2.0.0 or higher, and targeting devices running Android 4.0 (API level 15) and higher.
After deploying an app, a small, yellow thunderbolt icon appears within the Run button (or Debug button), indicating that Instant Run is ready to push updates the next time you click the button. Instead of building a new APK, it pushes just those new changes and, in some cases, the app doesn't even need to restart but immediately shows the effect of those code changes.