App Bundles
Table of Content:
An app bundle — officially called an Android App Bundle (AAB) — is Google's publishing format for Android apps on the Play Store. Introduced in 2018 and made mandatory for all new apps from August 2021, the AAB format replaced the traditional APK as the standard way to submit apps to Google Play. Rather than delivering a single large APK to every user, app bundles allow Google Play to generate and serve optimized, device-specific APKs — reducing download sizes and improving app performance for end users.
How Do App Bundles Work?
When a developer uploads an AAB to Google Play Console, they hand off the packaging and distribution work to Google. Google Play analyses the end user's device — its screen density, CPU architecture, and language settings — and assembles a lean APK containing only the code and resources that device actually needs. The result is a smaller, faster download compared to a traditional universal APK.
An Android App Bundle is made up of three core components. The base module contains the core app code and is always delivered at install. Feature modules are optional parts of the app that can be downloaded on demand — only when a user accesses a feature that requires them. Asset packs handle large media files, which is especially useful for games with heavy graphics or audio libraries.
One important requirement: developers must enroll in Play App Signing. Because Google generates the final APKs from the bundle, Google holds and applies the signing key to the distributed files. This is a trade-off — developers give up direct APK signing control in exchange for smaller, optimized downloads and access to advanced delivery features.
Dynamic Delivery — What It Means for Users
The engine behind app bundles is called Dynamic Delivery. Instead of every user downloading the same monolithic package, each user receives a version of the app compiled specifically for their device configuration. Google reports this typically reduces download sizes by 15–20% compared to equivalent universal APKs.
On-demand feature modules take this further. A navigation app, for example, can ship offline maps as a separate module that only downloads when a user explicitly requests it. A photo editor can hold back AI processing features until a user opens that tool for the first time. Users aren't penalized with a large install for features they may never use.
Play Feature Delivery and Asset Packs
Two advanced capabilities become available when using the AAB format that simply aren't possible with traditional APKs.
Play Feature Delivery lets developers control exactly when feature modules are delivered — at install time, on demand, or conditionally based on device features (for example, delivering an AR module only to devices with the right hardware). Play Asset Delivery is designed for large asset files and is the standard solution for games that would otherwise ship enormous APKs. Both systems are exclusive to the AAB format.
App Bundle vs. APK: Key Differences
The shift from APK to AAB is one of the more significant changes Google has made to the Android publishing process. Here's how the two formats compare:
Feature | App Bundle (AAB) | APK |
Required for new Play Store apps | ✅ Yes | ❌ No |
Device-optimized delivery | ✅ Yes | ❌ No |
Smaller download size | ✅ Yes | ❌ No |
On-demand feature modules | ✅ Yes | ❌ No |
Direct install from file | ❌ No | ✅ Yes |
Signed by developer | ❌ No | ✅ Yes |
Sideloading supported | ❌ No | ✅ Yes |
APKs haven't disappeared entirely. They're still the format of choice for sideloading, enterprise app distribution, and publishing on third-party Android stores like the Amazon Appstore or Samsung Galaxy Store. If your distribution strategy includes any channel outside Google Play, you'll still need to maintain APK builds alongside your AAB.
For Google Play, however, the AAB is now the only option for new submissions, and Google has been steadily encouraging existing apps to migrate.
Why App Bundles Matter for ASO
The connection between app bundles and App Store Optimization isn't immediately obvious, but it's real and worth understanding.
App download size is one of the friction points that costs installs. When a user taps "Install" and sees a large file size — especially on a mobile data connection — hesitation creeps in. Storage warnings, slow download progress, and data concerns all increase the chance a user abandons the install before it completes. By reducing the delivered APK size by 15–20%, app bundles directly reduce that friction at one of the most critical moments in the funnel.
There's also a listing-level effect. Download size is displayed on every Play Store app listing. A visibly smaller app can influence click-to-install decisions in competitive categories where users are comparing multiple options side by side.
On-demand modules add another layer: even complex, feature-rich apps can present a small initial footprint, then grow as the user engages more deeply. The app doesn't look intimidating at the install decision point, but nothing meaningful is missing once it's installed.
Tracking how changes to your app's download size — including the transition from APK to AAB — affect your install conversion rate over time is something tools like AppFollow can help with, monitoring Play Store listing performance and key ASO metrics in one place.
App Size and Install Conversion Rate
Google's own research has found a clear relationship between APK size and install rates: every 6 MB reduction in download size correlates with roughly a 1% improvement in install rate. At scale, that's a meaningful number.
The effect is amplified in markets where mobile data is expensive or device storage is limited. Users in India, Brazil, Indonesia, and similar high-growth markets are far more sensitive to app size than users in Western Europe or North America. An app that trims its install footprint with the AAB format isn't just making a technical improvement — it's actively expanding the audience it can reach.
App Bundles in Markets with Low Connectivity
If your growth strategy includes emerging markets, app size isn't a minor consideration — it's often a deciding factor in whether a user installs at all. Devices with 16–32 GB of total storage are still common in these regions, and users manage space carefully. An app that ships a 90 MB APK when it could deliver a 70 MB optimized package is losing installs that could have been won.
Market-specific conversion rates are visible in Google Play Console and in ASO platforms like AppFollow, making it straightforward to measure the real-world impact of app size changes across different geographies.
How to Create an App Bundle
Building an AAB doesn't require a fundamentally different development process — it's mostly a change at the build and submission stage.
In Android Studio, you generate an app bundle through Build → Generate Signed Bundle/APK → Android App Bundle. The process prompts you through signing configuration and produces a .aab file ready for upload. From the command line, the Gradle task is simply ./gradlew bundleRelease.
The .aab file is then uploaded to Google Play Console under your chosen release track (internal testing, closed testing, open testing, or production). Google Play's App Bundle Explorer lets you inspect exactly which APKs will be generated from your bundle and preview their sizes per device configuration — a useful sanity check before rolling out to production.
For local testing before submission, Google provides a command-line tool called bundletool that simulates the APK generation process and lets you install and test the generated APKs on a device or emulator. It's worth running this step, especially when testing on-demand feature modules for the first time.
One setup requirement to complete before any of this: Play App Signing must be enabled in your Google Play Console account. Google will manage the signing keys for the APKs it generates and distributes.
Limitations of App Bundles
App bundles are the right choice for Google Play distribution, but they come with constraints worth knowing before you commit fully to the format.
- Distribution is Google Play-only. An AAB file cannot be sideloaded or distributed through third-party stores. If you publish on the Amazon Appstore, Samsung Galaxy Store, or distribute APKs directly to enterprise customers, you'll need to maintain a separate APK build pipeline in parallel.
- Google controls app signing. Play App Signing enrollment is mandatory. Developers who prefer to control their own signing keys will need to adjust to this model. Google treats signing key security as a platform responsibility, and there are recovery options if keys are lost — but the signing process is no longer fully in the developer's hands.
- Apple App Store compatibility. Android App Bundles are entirely Android-specific. iOS apps use Apple's own App Thinning system, which achieves similar goals (sliced, device-optimized delivery) but through Apple's infrastructure using .ipa files. There's no shared format between the two platforms.
- Large games require additional setup. While Play Asset Delivery removes strict size caps, games with very large asset libraries still require careful module architecture to take full advantage of the system. The initial investment in structuring assets correctly pays off at scale, but it's not a zero-effort process.
Track Your ASO Performance with AppFollow
Switching to the Android App Bundle format is one step toward a better-performing Play Store listing. Track how your app size changes affect install conversion rates, keyword rankings, and user sentiment — all in one place with AppFollow.
Frequently Asked Questions About App Bundles
What is an app bundle?
An app bundle (Android App Bundle, or AAB) is Google's publishing format for Android apps on the Play Store. Instead of uploading a single APK that works on all devices, developers upload an AAB and Google Play automatically generates and serves optimized APKs tailored to each user's device — reducing download sizes and improving performance.
What is the difference between an APK and an app bundle?
An APK is a self-contained installation file that includes all code and resources for every device type. An app bundle is a publishing format that lets Google Play generate device-specific APKs, resulting in smaller downloads for users. Since August 2021, the AAB format is mandatory for all new apps submitted to Google Play, though APKs are still used for sideloading and third-party store distribution.
Are app bundles mandatory for the Google Play Store?
Yes. Google made the Android App Bundle format mandatory for all new apps submitted to Google Play from August 2021. Existing apps could continue submitting APKs, but new apps must use the AAB format. Google has continued extending the requirement over time to encourage all developers to migrate.
Do app bundles affect ASO?
Yes, indirectly but meaningfully. App bundles reduce download size by up to 15–20%, which can improve install conversion rates — particularly on mobile data connections and in markets where device storage is limited. Since app size is visible on the Play Store listing, a smaller install footprint can also influence a user's decision to install.
Can I use an app bundle for the Apple App Store?
No. Android App Bundles are a Google Play-specific format. Apple has its own equivalent technology called App Thinning (including Slicing and On-Demand Resources), which achieves similar goals but uses Apple's own formats and infrastructure.
How do I test my app bundle before publishing?
Google provides a command-line tool called bundletool that lets you locally generate the set of APKs your bundle would produce and test them on a device or emulator before submitting to Google Play. You can also use the App Bundle Explorer in Google Play Console to inspect generated APKs and their sizes per device configuration.
