If you're new to mobile development, build formats can feel confusing fast. You'll hear APK, AAB, and TestFlight thrown around — but what do they actually mean? Let's break it down.
Android: APK vs AAB
What is an APK?
An APK is the file format Android devices actually install and run. Think of it as a zip containing your entire app — code, images, resources — for every possible device.
When you build an APK it includes everything: code for different processors, images for different screen densities, strings for different languages, all packed into one file.
Use APKs when:
- Testing the app yourself
- Sharing directly with testers
- Distributing outside the Google Play Store
What is an AAB?
An AAB (Android App Bundle) is what you upload to Google Play — but users never see it directly.
When someone downloads your app, Google Play inspects their device and generates a custom APK containing only what that device needs. Smaller downloads, less wasted space.
The catch: AABs only work with Google Play. For direct distribution, you still need an APK.
Use AABs when:
- Publishing to the Play Store (Google now requires AABs for all new apps)
Quick reference
| Format | Who uses it | When |
|---|---|---|
| APK | You or your testers | Development, direct sharing |
| AAB | Google Play | Publishing to the Store |
iOS: TestFlight
What is TestFlight?
TestFlight is Apple's official beta testing platform. You upload your build to Apple's servers, invite testers, and they install it through the TestFlight app — no App Store submission needed.
Key limits to know:
- Builds expire after 90 days
- Up to 10,000 external testers per app
- Testers must accept an invite before installing
Keeping iOS builds lean
Apple applies App Thinning automatically, but you can still help:
- Use asset catalogs for images
- Exclude debug symbols from release builds
- Audit third-party libraries for size
The short version
- APK — what Android devices actually run; use during development and direct sharing.
- AAB — what you give Google Play; it creates the right APK per device.
- TestFlight — how you get iOS builds to testers before hitting the App Store.
Build with APKs, ship with AABs on Android. Test with TestFlight, release through the App Store on iOS.