Goodbye Giant APK: how we went from 186 MB to 62 MB with split-per-ABI (and three lines in CI)

Android-only, Firebase App Distribution, and plenty of ML under the hood.

This is a translation of the original post written in Spanish

186 MB… seriously?

Our universal APK weighed in like an elephant: 186 MB. And yes, the app only ships on Android (for now), but the pubspec.yaml carries some heavy hitters:

• firebase_analytics, firebase_messaging, firebase_ml_model_downloader
• google_mlkit_text_recognition + other vision libs
• camera, video_player, etc.

The test team complained about the download size in Firebase App Distribution, and I burned bandwidth every time I pushed a new build. We also have an internal flow that takes that same APK from FAD and redistributes it through MDM to several corporate user groups — nobody enjoys moving a 186 MB file for every update.

First discovery: our devices are 100 % ARM64

Google Analytics showed me something key: every phone in production (≥ 2020) runs an arm64-v8a chipset. No Intel Chromebooks, no 32-bit phones.

If your whole fleet is 64-bit… why ship 32-bit libraries?

The express fix: split-per-ABI

1. Minimal changes in android/app/build.gradle

android {
  splits {
    abi {
      enable true          // turn it on
      // this no longer generates the .apk the IDE expects; 
      // if you need debug builds you can do something like:
      // enable gradle.startParameter.taskNames.any { 
      //    it.toLowerCase().contains('release') && !it.toLowerCase().contains('debug') 
      // }
      reset()              // clear the default list
      include 'arm64-v8a'  // this architecture only
      universalApk false   // DO NOT build the giant universal APK
    }
  }
}

2. Build from the console (or your Fastlane/CI pipeline)

flutter build apk --release --target-platform android-arm64
# ↳ produces app-release.apk (~62 MB on my side)

(*--split-per-abi works too; I just upload the -arm64-v8a one.*)

3. Extra tweak in my CI pipeline (GitHub Actions + Fastlane)

- name: Enable Android Build Optimizations
  run: |
    echo "android.enableR8.fullMode=true"  >> android/gradle.properties
    echo "android.enableJetifier=true"     >> android/gradle.properties
    echo "org.gradle.caching=true"         >> android/gradle.properties

Just three lines and R8 does its shrinking and obfuscation magic.

Result

Firebase App Distribution

Summary of APK’s sizes

-124 MB without touching a single line of Dart, removing features, or fighting with ProGuard 🙌.

Why does it work?

• The APK contains one single folder /lib/arm64-v8a/ instead of three.
• Every Flutter & plugin .so is copied once, not three times.
• Dart AOT snapshots shrink as well.

If a 32-bit device shows up tomorrow, we rebuild with --split-per-abi and hand over the right APK. While our fleet stays ARM64, we enjoy the mini size.

Quick checklist

1. Check your device pool (GA4 → Device model).
2. If it’s 100 % 64-bit → add the splits { abi { … } } block.
3. Turn on R8 in CI with three lines.
4. flutter build apk --target-platform android-arm64
5. Upload to Firebase App Distribution (and in our case to the MDM — without feeling guilty about the MBs).

How heavy is your APK?

Let us know in the comments how big your build is right now 🤓👇 (If it’s over 100 MB, you already know where to start).

For more information

Flutter → Reducing app size Official guide on split-per-ABI, asset compression, and --target-platform.

[embed]Measuring your app's size How to measure app size for iOS and Android.docs.flutter.dev

Android → Shrink, Optimize, and Obfuscate your app Google docs on R8/ProGuard, shrinkResources true, keep rules, etc.

[embed]Enable app optimization | App quality | Android Developers Learn how to enable R8 to optimize your app size and speed.developer.android.com

Google Play → Play App Signing & Android App Bundles Why AABs deliver ABI/density-optimized APKs and speed up downloads.

[embed]About Android App Bundles | Google Play | Android Developers Important: From August 2021, new apps are required to publish with the Android App Bundle on Google Play. New apps…developer.android.com