One of the things that’s long set Android apart from iOS is that while both Google and Apple maintain app stores, Google makes it fairly easy for users to install apps downloaded from sources other than the Google Play Store. It’s a process commonly known as sideloading.

But starting later this summer, sideloading some apps could get a little more complicated.

That’s because starting in August, Google will require developers who publish apps to the Google Play Store to package them as Android App Bundles, or .aab files.

Up until a few years ago, when App Bundles were first introduced, installing an Android application meant downloading and installing a single APK (or .apk) file that contained all the code submitted by a developer… including code that you might not actually need for your device.

For example, if a developer’s app is designed to run on devices with ARM or x86 processors, you don’t necessarily need all the x86 code if you’re only installing it on your ARM-based phone. But it was probably included in the APK installer file anyway.

App Bundles are basically designed to let the Google Play Store separate out the components of an Android application into a set of “split APK” files, only delivering the ones you need for your device when you click the install button. That way you don’t end up downloading unnecessary code for display types, languages, or processor architecture.

The end result is generally a good thing for most Android users – you get smaller, faster downloads when installing apps through the Play Store.

But if you encounter an .aab file in the wild, you cannot just sideload it to your Android device using the same steps you’d use with an APK file. You can still install APK files, assuming the developer continues to provide complete APKs for their apps even after Google begins enforcing adoption of .aab for the Google Play Store.

But if developers only release .aab files moving forward, then there’s a chance that when you encounter APK files floating around the web, they may only contain some of the code necessary to install the full app on your device. They might not have support for your processor, language, or display for example if the APK was part of a larger bundle.

There are some third-party solutions that could make installation of App Bundles found outside the Play Store easier though.

For example, one of the most trusted places to download Android apps from outside the Google Play Store is APKMirror, a website maintained by the team behind the Android Police blog.

While you can download APK files directly from APK Mirror and sideload them onto an Android phone, tablet, or other device, the team also has an app called APKMirror Installer that allows you to install regular APK files as well as app bundles packaged in the .apkm, .xapk, or .apks formats.

So you may need an app to sideload some Android apps moving forward. But not necessarily all Android apps.




New apps 

on Google Play


Android App Bundle (AAB)

Expansion files (OBBs)

Play Asset Delivery or 

Play Feature Delivery

Updates to existing apps

No change

New instant experiences

Instant app ZIP

Instant-enabled Android App Bundle (AAB)

Updates to instant experiences

Google is only requiring developers to use the new .aab format for new apps submitted to Google play starting in August, 2021. Developers with older apps have a choice of adopting the new format when delivering updates, or sticking with old school APK files. And many apps that may never have been available in the Play Store in the first place will likely continue to be available from other sources such as APKMirror and F-Droid as APK installers.

That said, Android App Bundles have been around since 2018, and Google says more than a million apps in the Google Play Store already use app bundles, including “the majority of the top 1,000 apps and games on Google Play.” So it seems likely that app bundles are here to stay.

If you only install apps from the Play Store, that’s probably not a bad thing. If you’re a regular sideloader, then you may want to check out APKMirror Installer or other third-party solutions that will help you install app bundles if and when you encounter them.

But there is one other issue related to Google’s push for .aab files to become the new standard for apps distributed via Google Play that is causing concern among some security experts: the way apps are signed (so that you can trust that the app you’re installing is the same as the one the developer distributed).

When a developer uploads an App Bundle to Google Play, Google will automatically generate the split APK files that will eventually be downloaded to user devices — and those APK files are signed by Google rather than by the developers who created them. And that means that there’s essentially a single point of failure – if Google’s servers are breached then it’s hypothetically possible that an attacker could obtain the private keys used to sign thousands of even millions of Android apps… which would allow them to pass off fake versions of those apps that look to Android devices as if they were authentic.

Sure, Google has a pretty strong vested interest in preventing data breaches. But as we’ve learned time and time again, no company is 100% immune.

via Android Developers Blog, xda-developers, and CommonsWare

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6 replies on “Sideloading some Android apps could get more complicated as Google pushes Android App Bundles”

  1. But isn’t APKMirror a gray market website? Those apps aren’t even uploaded by the publisher.

    1. I also always assumed that was the case. I just checked out their FAQ, and they claim that they never upload pirated or paid apps. But that doesn’t exactly answer the question.

      The fact that their upload process doesn’t ask any questions to confirm that the uploader is the original owner, I guess we need to assume that many of their APKs were not provided by the original owner.

    2. I think you’re right, but there are legitimate ways to get APKs. I tend to install apps on my device and back up the APK so I have options if an update breaks, the app is pulled, or for devices on which I don’t use play services. Now, there’s a chance my backed-up APKs won’t contain the right code for any device other than the one on which I downloaded them.

  2. Single point of failure however shields the developers from a “developer point of failure”. So like if Google is breached, its a single fix, rather than nagging busy developers flying blind, with their stuff passed off as fake versions. Thats a management nightmare.

    1. Now, instead of only being subject to developer failure, you are also at risk of Google failure. You can still be in trouble if the developer messes up because the developer has the ability to push code updates which Google will now sign for them. With this, you’ve just added another possible failure without fixing, in any way, the risk of developer failure.

  3. Oh dear, how can these big tech companies just keep on dissapointing me. I don’t use Play Store and never will. I only use F-Droid, the only way to get apps and be sure they don’t consist entirely of tracking code, so I hope that can stay working. Either way, time to get a Pinephone and get rid of all bother and complications.

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