Good news for end-users, but incoming changes for developers.

The APK app format has been a around for as long as Android apps existed, but in 2018, Google announced they would support a new format called Android App Bundles (*.abb) which would result in smaller app file sizes.

Google recently announced that the AAB file format will officially replace Android APKs starting in August. To be clear, every app a developer uploads to Google Play in August must come in this new file format. Apps that are currently hosted on Google Play as APKs can remain that way.

What are ABBs for?

Android App Bundles can be 15% smaller than APKs, this means faster downloads for end-users.
Also, developers will have more control about how they distribute their apps, packages and updates, which will result in more flexibility on their side too.

Upcoming issues, and exceptions

Developers submitting their app to other distribution channels such as Samsung or Amazon will need to manually export APK versions of their apps. So developers posting to multiple channels will anyway need to keep both file formats available for distribution.
Also, sideloading or uses through EMMs will only work with APKs, as AAB is reserved to the Google Play…public store. Google Play’s private, or work channel (Android Enterprise) still support APK files.

If your development workflow or CI is exporting to AAB only and if you wish to support other distribution channels, this means that you will need to share your app signing key with a third-party if you want them to export an AAB to an APK.