What is an Android App Bundle and its advantages over APK?

WHAT THIS TESTS: Whether the candidate understands the shift from monolithic APK distribution to modern Google Play publishing. It checks if they know that an Android App Bundle is a publishing format rather than a runtime installation format, and whether they grasp the server-side optimization that happens inside Play. The interviewer wants to see awareness of how build artifacts relate to user experience, specifically install size and dynamic delivery.

A GOOD ANSWER COVERS: First, define an AAB as the official publishing format for Google Play that includes all compiled code and resources for a project in a single upload artifact. Second, explain that Google Play processes the bundle to generate and serve optimized APKs for each unique device configuration, meaning users receive only the language resources, screen density assets, and device-specific native libraries their device actually needs. Third, highlight the concrete benefit of smaller download and install sizes compared to a universal APK that contains every variant. Fourth, mention that the format enables advanced distribution through Play Feature Delivery and Play Asset Delivery, which allow modular features and large assets to be delivered on demand rather than at install time.

COMMON WRONG ANSWERS: Calling an AAB a compressed APK or a renamed ZIP file misses the architectural point entirely. Another red flag is claiming the Android device installs the AAB directly; in reality, devices install APKs generated from the bundle. Candidates who describe the advantage as only signing or security improvements without mentioning device-specific optimization show shallow knowledge. Confusing AAB with Android Instant Apps, or suggesting it is only useful for very large apps, are also weak signals that the candidate has not worked closely with modern Play distribution.

LIKELY FOLLOW-UPS: How does Play Feature Delivery work under the hood, and how do dynamic feature modules relate to the base module? What is the role of the base module, and what constraints does it have? How would you test a bundle locally before uploading to Play, using bundletool or the Play Console internal testing track? What happens if a user sideloads an app rather than installing from Play, and how does that affect dynamic delivery? How do you handle versioning when moving from multiple APKs to a single app bundle?

ONE CONCRETE EXAMPLE: Imagine an application that supports five languages, four screen densities, and three CPU architectures. A universal APK might ship every combination to every user, resulting in a large file. With an AAB uploaded to Play, the store generates a device-specific APK containing only the French strings, xhdpi drawables, and the matching native libraries for a user on that device, cutting the download size significantly compared to the universal alternative.