An app bundle is what you upload. An APK is what gets installed.
An Android App Bundle, the .aab file, is a publishing format. An APK, the .apk file, is the installable one. Google's own frequently asked questions page says it in a single line: app bundles are only for publishing and cannot be installed on Android devices. You upload one bundle, Google Play works out what a particular phone needs and builds the APKs for it, and the phone installs those. Since August 2021 a new app on Google Play has had to be published as a bundle, so for most people the decision was made years ago. What is left to decide is when you still need an APK, and the short answer is whenever a human has to tap the file. People usually meet this a week after publishing to the App Store and finding that Android works nothing like it.
Below: what each format is, who is still allowed to ship an APK, the size difference that Google documents and the one it does not, and how to get a bundle onto a device you are holding. Every figure here was read on Google's pages on 21 October 2026, with the page dates next to it.
See which file you actually needThe short version
You upload one file. Google Play builds the rest.
An app bundle is a single upload that carries your compiled code and every resource for every device your app supports. Google Play opens it, decides what one particular phone needs, and generates a small set of APKs for that phone: a base APK, plus configuration APKs for its screen density, its chip architecture and its language. The phone installs that set. You never see the files unless you go looking for them in the App bundle explorer in Play Console. Google's own phrase for this arrangement, on the About Android App Bundles page last updated 24 June 2026, is that the format defers APK generation and signing to Google Play.
An APK is the other end of the same pipe. One file, everything in it, and the only thing an Android phone knows how to install. That is why these two are badly described as alternatives. One is a submission, the other is what the submission produces. The useful question is which of them you need in your hand right now, and that depends entirely on whether a store or a person is doing the installing.
What is the difference between an app bundle and an APK?
Google answers this one itself, and the answer is shorter than most of the articles about it. App bundles are only for publishing and cannot be installed on Android devices. The Android package, APK, is Android's installable and executable format for apps. App bundles must be processed by a distributor into APKs so that they can be installed on devices. That is the whole distinction, and every other difference follows from it.
Some background that changes how you treat the format. The bundle launched in 2018. It is not a Google Play private arrangement: Google says the app bundle is open source, that any app store can support it, and that some other stores already do. It is supported by Android Studio, Bazel, Buck, Cocos Creator, Gradle, Unity and Unreal, so whatever your project is built with, there is a path to producing one. And it is no longer a minority format. Google states that over 1 million apps and games publish their production releases on Google Play as app bundles.
The part that surprises people is the signing. Because Google Play builds the APKs, Google Play has to sign them, which means Play App Signing comes with the bundle. Google's FAQ says Play App Signing is required for new apps so that they can use bundles. You keep an upload key, you sign the bundle with it, and Google verifies you from that. Google holds the app signing key and signs the real APKs. If an upload key is lost or stolen, Google can reset it. The app signing key is the one that cannot be replaced casually, and handing it to Google is the trade the format asks you to make.
One consequence of that trade bites later, usually in production. Any service that checks your app's certificate, a maps key, a social sign-in, a push service, has to be given the fingerprint of the key that signed the file on the user's phone. That is Google's app signing key, not your upload key. Register the wrong one and the feature works perfectly on your own device and fails for everyone who installed from the store.
Check yours
Which file do you actually need?
Tick what you are trying to do. The answer depends on who installs the file, not on which format is newer.
Nothing ticked. Most teams need both files in the same week: a bundle for the store and an APK for the person sitting next to them.
Can you still publish an APK to Google Play?
Not for a new app. The note at the top of Google's About Android App Bundles page, which carries a last updated date of 24 June 2026, states that from August 2021 new apps are required to publish with the Android App Bundle on Google Play. The same note adds that from June 2023 new and existing TV apps are required to be published as app bundles, which is the one deadline people miss, because it reaches back and applies to apps that were already live.
Older apps kept their grandfather rights. An app created before August 2021 that has always shipped APKs can carry on shipping them, and Play Console Help is blunt about the price of staying there: apps still publishing with APKs instead of app bundles are subject to the legacy APK size limits, meaning a maximum APK size of 100MB, and not to the bundle limits. If you ever want to move, Google documents a key upgrade path for apps created before August 2021, and it has a cost of its own. After the upgrade, every release has to contain two things: an app bundle, and a legacy APK signed with your old key, so that existing installs keep updating while new installs move to the new key.
Private and managed distribution is a separate rule worth reading carefully if you are shipping to one company rather than the public. Google says private apps published to managed Google Play from Play Console are required to publish app bundles, and then notes that publishing APKs is still supported through the Managed Play iframe. Two routes to the same audience, two different answers.
None of this changes what the store costs you. Google Play charges a one-off registration fee and Apple charges annually, and the format of your upload has no bearing on either, which is worth confirming before you budget. The cost to publish an app breaks down what each store actually bills.
How much smaller is an app bundle, really?
Almost every article on this quotes a percentage. Google does not. We read the three pages where an average saving would sit, About Android App Bundles, the Android App Bundle frequently asked questions, and the Play Console article on app size limits, on 21 October 2026. None of them states a percentage. What the About page says is that users get smaller and more optimized downloads, with no figure attached. If you see a specific number quoted as Google's, it is coming from somewhere other than Google's current documentation, and it is probably years old.
The documented difference is a limit, and it is large. Play Console Help gives the bundle ceilings as a table: 500MB for a base module, 500MB for an individual feature module, 1.5GB for an individual asset pack, 4GB cumulative for all modules and install time asset packs, and 30GB cumulative for asset packs delivered on demand or fast follow. The total maximum compressed download size for an app published on Google Play is 34GB. Against that, an app still publishing APKs is capped at 100MB. The reason you are allowed more is that no single device downloads all of it.
Three numbers from the same page change how you plan a large app. Every Play size limit is measured on compressed download size, which Play Console calculates when you upload, and which bundletool will estimate locally with a similar but not identical calculation. An app over 1GB must target a minimum SDK version of Android Lollipop, API level 21, or higher. And an app above 200MB makes anyone installing on a mobile data connection see a non blocking dialog warning them about the size. That dialog is the real size limit for most consumer apps, because it is the point where installs start going elsewhere. The iOS side has a harder version of the same problem, which the ios app size limit cellular guide covers.
Two more limits sit underneath, and they only matter if you are splitting a big app up. The maximum recommended number of feature modules is 100 if your minimum SDK is Android Oreo, API level 26, or higher, and 50 below that. The maximum number of asset packs in one bundle is 100. Expansion files, the old .obb mechanism, are not an option here at all: Google says Play does not support expansion files for bundles and calls them a legacy Play specific solution for publishing large apps with APKs. Apple splits downloads a different way, which app thinning and size limits goes through.
Play Console Help, Google Play maximum size limits table, read 21 October 2026
Can you install an AAB directly on a phone?
No, and there is no file manager trick that gets around it. Google states that app bundles cannot be installed on Android devices and must be processed by a distributor into APKs first. Normally that distributor is Google Play. When you are testing, you do the same job yourself with bundletool, which is the tool both Google Play and the Android Gradle plugin use. You generate an APK set from the bundle, either for every configuration your app supports or for one connected device, and then deploy that set.
Android Studio hides the same steps behind a setting. In Run and then Edit Configurations, change Deploy to APK from app bundle, and the IDE builds the bundle and installs only the APKs your connected device needs. Google's documentation warns that this is slower than building and deploying an APK on its own, which is why it is not the default. Play Console Help offers a third route: download the device specific APKs from the App bundle explorer and install them with adb install-multiple, which is the closest you can get to seeing exactly what Google Play would have delivered.
This is where split APKs turn into a support problem. The About Android App Bundles page warns that partial installs of sideloaded apps, meaning apps installed outside the Google Play Store that are missing one or more required split APKs, fail on all Google certified devices and on devices running Android 10, API level 29, or higher. Google also notes that an APK optimized for one device, for a particular chip architecture, for instance, may not work when it is copied straight to a different device. If you are sending builds to testers by hand, send one APK that covers every configuration and skip the whole category of problem.
One myth to retire. Bundles do not stop sideloading. Google answers that in as many words: app bundles do not prevent users from installing APKs from any source, because the bundle is a publishing format and does not change how the Android platform works. Your project can still produce a plain APK on the same afternoon it produces a bundle, and Google says as much when it tells you that you can build both at the same time for stores with different requirements.
The two formats, line by line
| The question | App bundle, .aab | APK, .apk |
|---|---|---|
| What the format is for | Publishing only | Installing and running |
| Can be installed on an Android device | No | Yes |
| Accepted for a new app on Google Play | Yes | No |
| Who signs the files a user receives | Google Play, using the app signing key it holds | You, before the file leaves your machine |
| Download size ceiling on Google Play | 500MB base module, 4GB per device | 100MB, the legacy APK limit |
| Expansion files, the .obb kind | No | Supported, and Google calls them legacy |
| Holds every device configuration at once | Yes | Yes |
| What a phone ends up with after install | A base APK plus configuration APKs | The one APK you handed it |
Figures read from Google's documentation on 21 October 2026. The size row is the one most likely to move, so check it before you plan around it.
Where this lands if a builder generated your app
Nothing about the formats changes because an AI wrote the code. The store still wants a bundle, the tester on the sofa still wants an APK, and Google Play still holds the signing key either way. What does change is how much of that plumbing you have to assemble yourself before you can see a build on a real phone.
Newly is an AI app builder. You describe an app in plain English and it writes a real React Native and Expo project in TypeScript that you own, with two-way GitHub sync so the code is never trapped. On Android it does both jobs: it publishes to Google Play internal testing, which is the bundle route, and it builds a standalone Android APK, which is the file you send to a person. On iOS it uploads to TestFlight. It does not submit to the App Store for you, because Apple requires the owner of the content to submit it. It is $25 a month, with no free tier.
Because the project underneath is a normal Expo project, the Android behaviour is the behaviour Expo documents. Its build reference page on APKs, modification date 8 October 2025, says the default output of an Android build is an app bundle, that bundles cannot be installed directly on a device, and that you get an APK instead by setting android.buildType to apk, distribution to internal, or developmentClient to true in a build profile. That is the lever, and it stays available to you after the generator has finished, because the configuration file is in your repository rather than inside someone else's product.
Questions people ask about app bundles and APKs
Google's own Android App Bundle FAQ, read on 21 October 2026 and carrying a last updated date of 6 October 2026, answers it in three sentences. App bundles are only for publishing and cannot be installed on Android devices. The Android package, APK, is Android's installable and executable format for apps. App bundles must be processed by a distributor into APKs so that they can be installed on devices. So a bundle is a submission and an APK is the thing that runs. Google Play opens your bundle and builds the APKs each device needs, which is what Google means when it says the format defers APK generation and signing to Google Play.
Build it once, ship it in both shapes
Decide early who installs your build by hand and who installs it from a store. That one answer tells you which file you need, and it saves a week of reading about a format war that does not exist.
Start building