Developers must start using Android App Bundle in August.

The result will be smaller file sizes.
What is APK?
Since Android started, Android apps are released in the Android Package (APK) format. But in 2018, Google launched Android App Bundles or AAB.
It’s a new format that allows an app to run across a range of Android devices.
Creating an app can be tedious. It has several challenges.
After creating codes and optimizing resources, developers still end up with a bloated APK full of code and resources.
Worse, it includes assets that users don’t need.
The APK size affects people directly who install the app after they visit the Google Play page. Every time there’s a 6MB increase in the APK size, expect to see a decrease in the installation conversion rate.
Benefits of Android App Bundle
The Android App Bundle supports a range of Android devices while it reduces APK size. Android developers can just publish an AAB and let Google Play do the rest.
After uploading the AAB file, Google Play will generate a base APK that contains all the code and resources to provide the app’s base functionality.
Every time a person downloads the app, Google Play will utilize the new Dynamic Delivery serving model. This will help in delivering a configuration APK customized for the device’s configuration.
Building an App Bundle reduces the size of the APK. This is its major benefit.
By publishing the app as a Bundle, it ensures that it works on as many devices as possible.
Thus, if developers build multi-APKs before, they can simplify the process through Bundles.
Instead of facing the potential for error and complexity of maintaining different APKs, developers can just build a single AAB file and allow Google Play to handle the rest.
Comes with Restrictions
But AAB has restrictions.
For instance, the APKs from the App Bundle must be smaller than 100MB. Devices that run Android 4.4 and earlier aren’t compatible with split APKs.
In that case, Google Play will serve App Bundle to those devices through multi-APKs.
Although AAB has several benefits, this format is only used by Google Play. It means that app redistribution will become complicated.
The release of this new format comes days after Microsoft released Windows 11. The new Microsoft OS lets users sideload Android apps as APKs.
As Google replaces APKs with Bundles, fewer apps will run on Windows 11. However, you can still obtain Android apps on your Windows 11 through the Amazon Appstore.
The need to use AAB will only apply to new apps. All existing apps are exempted. Private apps also don’t need to use AAB.
“There are now over 1 million apps using app bundles in production, including the majority of the top 1,000 apps and games on Google Play such as Adobe, Duolingo, Gameloft, Netflix, redBus, Riafy, and Twitter.”
Using an app bundle requires little work, according to Google. It’s just a matter of choosing an option at build time and test it as normal. Major build tools and other engines support this format.