For years Android apps have been distributed using APK files,
An APK contains a complied version of an android app.
Along with all of the app resources. Such as icons, sounds, language configurations
And more.. This is a bit of a problem, Because Android runs on thousands
of devices covering a huge range of screen sizes, performance baselines, and CPU architectures.
In May 2018, Google launched a new distribution format called Android App Bundles (AABs).
Android App Bundles play the same role as APKs. But with a few upgrades.
What are these upgrades?
Usually when we want to distribute a new or exiting app to Google Play.
We generate a signed APK that contain all of our app resources,
For all of those different device sizes and languages.
Resulting in large APK files with resources that aren't really needed on the users device.
With Android App Bundles, This is no longer an issue.
When you upload an AAB file to Google Play and a user installs your app,
Google play generates a signed APK containing only the resources and assets needed for
that specific device. Resulting in a 15% smaller APK file, Faster downloads,
Witch can lead to more installs.
With Android App Bundles you can also package on demand features in your app.
And use Google Play's Play Feature Delivery to deliver a feature to a user.
And for game developers with lots of assets, There's the Play Asset Delivery.
Witch Reduces user waiting time by dynamically delivering large assets while cutting delivery costs.
Who Should distribute using AABs.
Any new apps are required to upload AABs when publishing an app.
Existing Apps are still able to upload APK's to Google Play.
But I'm pretty sure this will change soon, So I recommend you get started ASAP.
For more information on Android App Bundles