Android App Bundle (AAB)
Also known as: aab vs apk, app bundle format, android app bundle
An Android App Bundle (.aab) is the publishing format developers upload to Google Play. Play uses it to generate and sign optimized APKs tailored to each device, so users download only the code and resources their phone actually needs.
- An .aab is uploaded to Google Play but never installed directly — Play generates optimized split APKs from it.
- Since August 2021, new apps published on Google Play must use the AAB format.
- Split APKs deliver only the density, CPU architecture, and language a given device needs, shrinking download size.
What an AAB contains
An AAB is a signed archive that bundles all of an app's compiled code and resources, but unlike an installable APK it is never run directly. Inside it holds a base module, optional feature modules, asset packs, and a `BundleConfig.pb` that tells Google Play how to split things up.
When a user installs, Play runs bundletool to build split APKs from the bundle: a base APK plus configuration APKs carrying only the matching screen density (drawables), CPU architecture (native `.so` libraries), and language resources. This is called Dynamic Delivery, and it is the reason an AAB-based install is usually smaller than a universal APK that ships every variant at once.
AAB vs APK and why size shrinks
The APK is the format a device installs and the OS executes; the AAB is purely an upload/publishing artifact. Since August 2021, new apps on Google Play must be published as AABs. With Play App Signing, Google holds the app signing key and re-signs the generated APKs, so the bundle you upload is signed only with your upload key.
Because each device receives just one density, one ABI, and one language set instead of all of them, the on-disk footprint and download size drop noticeably. A phone storage cleaner like Cleanor sees the result of this on the user's side: the installed app and its app cache are smaller, while older sideloaded APKs or leftover split files can linger as junk files in the Downloads folder.