If your React Native or Expo Android compilation suddenly crashes with a massive terminal stack trace pointing to an "unsupported class file major version" or claims a class file has the wrong version (e.g., wrong version 65.0, should be 61.0), your environment is caught in a silent version mismatch.

This error almost always triggers right after you upgrade your Expo SDK, bump your React Native core version, or update Android Studio.

Here is exactly why this happens, how to decode the cryptic internal version numbers, and how to get your build compiling cleanly.

Why Did This Happen Suddenly?

When React Native or Expo upgrades their framework architecture, they also upgrade the required version of the Android Gradle Plugin (AGP) inside your project.

Each version of AGP requires a strict minimum version of the Java Development Kit (JDK) to run the compilation pipeline. If your system's global terminal runtime environment or your IDE is still pointing to an older Java runtime, the build engine throws an immediate exception during the semantic analysis phase.

The Version Decoder Cheat Sheet

Java’s compiler doesn't map version numbers logically to their public marketing names. When the Gradle stack trace throws a decimal number at you, use this index to figure out what version your code is demanding:

• Class file major version 66.0 = Requires Java 22
• Class file major version 65.0 = Requires Java 21 (Common in newer 2025/2026 native modules)
• Class file major version 61.0 = Requires Java 17 (The baseline standard for modern React Native)
• Class file major version 55.0 = Requires Java 11 (Legacy)

If your terminal says wrong version 65.0, should be 61.0, your build script encountered a dependency compiled for JDK 21, but your system is executing the build toolchain using JDK 17.

Step 1: Find the Exact Path to Your Target JDK

Before making adjustments, you need to locate where the correct JDK version is actually installed on your machine.

On macOS

If you use Homebrew or standard installers, your JDK runtimes are stored under the virtual machine path. You can list all installed environments by running:
/usr/libexec/java_home -V

Copy the path to the required version. It will look similar to this:
/Library/Java/JavaVirtualMachines/zulu-17.jdk/Contents/Home

On Windows

By default, standard Java installers or Android Studio bundle their JDK environments inside program directories. Check these common locations:

• C:\Program Files\Java\jdk-17\
• C:\Program Files\Android\Android Studio\jbr\ (Android Studio's embedded Java runtime)

Step 2: Apply the Explicit Project Override (Recommended)

Instead of fighting global system environment variables that might break older projects on your machine, you can force this specific React Native project to use the correct runtime directory.

1. Navigate to your project's native android folder: cd android
2. Open the gradle.properties file.
3. Add the following property at the bottom, supplying the absolute path you copied in Step 1:

org.gradle.java.home=/Insert/Your/Actual/Target/JDK/Path/Here

(Note: Windows users must escape backslashes in this file, format it like: C:\\Program Files\\Java\\jdk-17)

Step 3: Align Android Studio with Your Terminal

A massive source of frustration is when the project builds fine in the terminal via CLI, but crashes the second you open it in Android Studio (or vice versa). You must align the IDE's build path:

1. Open your project folder inside Android Studio.
2. Navigate to Settings (or Preferences on macOS) > Build, Execution, Deployment > Build Tools > Gradle.
3. Locate the Gradle JDK dropdown menu.
4. Change it from the default system runtime to match the exact version your project requires (e.g., JDK 17 or JDK 21).
5. Click Apply and hit Sync Project with Gradle Files.

Step 4: Clear the Aggressive Build Cache

Gradle caches compilation footprints deeply. If you change your Java version without clearing the cache, Gradle will try to read the old, mismatched class files and throw the same error again.

Wipe the execution deck completely by running these commands in your root directory:

Clean the native android directories

cd android
./gradlew clean

Return to root and clear bundler caches

cd ..
npx react-native start --clear

Once the development server reboots and paths match up seamlessly across your terminal, properties file, and IDE, run your run command (npx react-native run-android or npx expo run:android) and the version mismatch error will be gone.