Shrink and optimize Unity code with R8

Although your core game logic in Unity is written in C# (compiled with IL2CPP), Android builds include substantial Java and Kotlin bytecode (classes.dex) to handle UnityPlayerActivity lifecycle events, Google Play services, billing, ads, and social SDKs.

Enabling R8, the default code shrinker and optimizer in the Android Gradle Plugin (AGP), removes unused classes and methods and optimizes bytecode. This not only decreases your app download size, but also reduces the runtime memory footprint of memory-mapped (mmap) DEX pages and baseline Java process overhead, mitigating physical memory pressure and low memory killer (LMK) terminations. Google Play also monitors your game's DEX optimization levels through the DEX code optimization metric in Android vitals.

Default behavior and Unity version support

In Unity, code minification is disabled by default (false) for both Release and Debug builds when creating a new project.

Unity first introduced R8 as an optional toggle in Unity 2020.1.0f1. Starting in Unity 2022.2.0f1 (and backported to Unity 2021.3.41f1 LTS), Unity upgraded its bundled toolchain to AGP 7.1.2+, removed legacy ProGuard support, and runs R8 exclusively whenever minification is enabled.

Enable R8 in Player Settings

To enable R8 code shrinking and optimization for Release builds:

1. In the Unity Editor, open Edit > Project Settings and select Player.
2. Select the Android tab and expand Publishing Settings > Build.
3. Under the Minify section, configure the options for your Unity version:
   • Unity 2021.3.41f1+ and 2022.2.0f1+: Select Release. Unity runs R8 automatically during the minifyReleaseWithR8 Gradle task.
   • Unity 2020.1.0f1 to 2021.3.40f1: Select both Release and Use R8.

If you automate builds using C# Editor scripts, configure these properties through PlayerSettings.Android:

using UnityEditor;

public static class AndroidBuildConfig
{
    public static void EnableR8ForRelease()
    {
        PlayerSettings.Android.minifyRelease = true;

        // Required only in Unity 2020.1.0f1 to 2021.3.40f1 and 2022.1 or earlier
        // (In Unity 2021.3.41f1+ and 2022.2+, R8 is always used when minification is enabled)
#if !UNITY_2022_2_OR_NEWER
        PlayerSettings.Android.minifyWithR8 = true;
#endif
    }
}

Add keep rules for JNI and reflection

Java classes and methods invoked dynamically from C# scripts using AndroidJavaClass or AndroidJavaObject have no static Java call sites. Without explicit keep rules, R8 might consider these classes unused and strip or rename them.

To preserve your custom Java bridges:

1. In Project Settings > Player > Android > Publishing Settings > Build, enable Custom Proguard File.
2. Open the generated Assets/Plugins/Android/proguard-user.txt file.
3. Add -keep rules for classes accessed over JNI or required by third-party plugins:

# Keep custom Java classes invoked from C# using JNI bridges
-keep class com.example.yourgame.** { *; }

# Keep callback interfaces passed between C# and Java
-keep interface com.example.yourgame.IPluginCallback { *; }

Troubleshoot common issues

This section describes how to resolve common build and runtime issues when using R8 in Unity.

Missing classes detected while running R8 build errors

In Unity versions using AGP 7.0 and higher (2021.3.41f1+ and 2022.2+), R8 enforces strict missing-class checks. If a build fails with this error, inspect the generated missing_rules.txt file in your build output directory (under Library/Bee/Android/Prj/.../build/outputs/mapping/release/missing_rules.txt or Temp/gradleOut/...) and add the required dependencies or rules to proguard-user.txt. For more information about writing keep rules, see Customize which code to keep.

R8 full mode compatibility with third-party plugins

In AGP 8.0 and higher (Unity 6+), R8 full mode is enabled by default to perform more aggressive optimizations. If a legacy Android plugin fails at runtime due to reflection issues, update the plugin's ProGuard rules or revert R8 to compatibility mode:

1. In Publishing Settings > Build, enable Custom Gradle Properties Template.
2. Open Assets/Plugins/Android/gradleTemplate.properties and add the following property:

android.enableR8.fullMode=false