Android App Bundles are replacing APKs - why it matters [UPDATE]

Google Play Store is constantly evolving to meet the growing needs and demands of Android users and developers. Many of those improvements rely on automated systems powered by AI and machine learning, particularly in screening apps for malware or prohibited content. There are times, however, when changes require developers to make changes in the way they write and distribute their apps. One of the most disruptive changes is coming in August when Google Play Store switches to App Bundles instead of APKs as its standard package format, a change that will affect not only developers but also Android users, hopefully for the better.

The What and Why of App Bundles

Short for Android Packages, APKs have long been Android's standard package format for apps and games. More analogous to Java's JAR archives (and is, in fact, an extension of it), APKs are designed to bundle everything that an app needs to be installed on a device, from code to assets like images and sounds, some of which would have different versions for different kinds and sizes of devices. As Android's ecosystem grew, however, so did the number of things that needed to be packaged in an APK for it to even work.

APKs, however, didn't scale well to Android's growth and Google had to make workarounds for larger apps, particularly games that sometimes needed gigabytes of additional data. That workaround came in the form of OBBs that needed to be downloaded even before you could start playing a game or using the app. These are the problems that Android App Bundles are promised to solve, and while the changes should be transparent to users, they should still be very noticeable.

Android App Bundles, which may be shortened to AABs, will change the way Android apps are packaged and, more importantly, delivered. One of the most immediate differences is that there will no longer be the need for a single APK to contain everything for all kinds of Android devices, meaning package sizes should be smaller and download times should be faster. In fact, App Bundles require that apps should be no bigger than 150MB.

New ways to deliver the same things

For apps that need more than 150MB, App Bundles introduce a new feature to replace OBBs called Play Asset Delivery. Using better data compression and dynamic delivery strategies, this PAD system promises faster downloads for non-code assets as well, perhaps even while already playing the game. Future updates can also be smaller because PADs won't contain all the new assets but only what changed between different versions of the assets, a.k.a. their deltas. Play Asset Delivery also comes with the benefit of security since the assets are stored in and downloaded from Google Play rather than some CDN hosting provided arranged by developers on their own.

Another new feature enabled by Android App Bundles not possible with APKs is the Play Feature Delivery. It extends the concept of App Bundles containing only the parts of the app that are needed on a particular device but focuses on features that are needed to actually start using the app as soon as possible. The idea is that it would allow users to immediately use the app just seconds after installing it, delaying the download of other parts of the app for later.

Android users shouldn't need to do anything on their end to benefit from these changes, though app developers have to do the heavy lifting for their part. Fortunately for them, Google Play Store's Android App Bundle requirement, which becomes effective in August, only applies to new apps submitted to the app store. Of course, developers can voluntarily also adopt App Bundles if they want to improve the experience for users.

The Catch: It's Google's World

This definitely sounds great, at least for users, but it does come with one subtle fine print. All of these features are available only on Google Play Store, which sounds like a no-brainer but has important implications for some Android developers. Unlike APKs, Android App Bundles cannot exist outside of Google Play and cannot be distributed outside of it. This means that developers switching from APK to App Bundles can no longer provide the exact same package or experience on other app sources unless they opt to maintain a separate APK version. This naturally puts third-party app stores at a disadvantage, but Google will most likely play up the Play Store's security as a major reason to avoid those sources anyway.

UPDATE: Google reached out to us with some clarifications on the relationship between APKs and AABs. In a nutshell, the Android App Bundle is a new publishing format that Google Play will use to generate APKs specific to your device and has support for those new, dynamic experiences such as Play Asset Delivery and Play Feature Delivery. Google says that it also provides developers ways to download a secure APK version to be distributed on other app stores or sideloaded directly by users.

In other words, AABs won't mean such apps can no longer be distributed in other app stores or as APKs, which is definitely great news for third-party app repositories. That said, there are still features like asset delivery and feature delivery that are tied to Google Play, so don't expect to find those when downloading apps from other stores.