React Native 0.84 is here, and it brings significant changes that streamline development and boost app performance. This release introduces several defaults and removals that simplify your workflow. Let's dive into the most important updates through common questions developers are asking.

What Is Hermes V1 and Why Is It Now the Default JavaScript Engine?

Starting with React Native 0.84, Hermes V1 becomes the default JavaScript engine on both iOS and Android. This follows an experimental opt-in phase in version 0.82. Hermes V1 is the next major evolution of the Hermes engine, featuring improvements to both the compiler and virtual machine. The result is measurably better JavaScript performance—faster execution times and lower memory usage for your apps.

If your app is already using Hermes (which has been the default since 0.70), you’ll automatically receive these benefits without any configuration changes. No migration is needed. The upgrade is seamless, giving you performance gains out of the box.

However, if you need to opt out for compatibility reasons, you can force the installation of the legacy hermes-compiler package via package manager overrides, set environment variables on iOS, or add a gradle property on Android. See the detailed instructions below.

How Can I Opt Out of Hermes V1 If Needed?

Opting out is handled differently per platform. For all package managers (npm, Yarn, pnpm), you can add an override or resolution in your package.json to force the legacy hermes-compiler version, e.g., "0.15.0". On iOS, when installing CocoaPods dependencies, pass the environment variables RCT_HERMES_V1_ENABLED=0 and RCT_USE_PREBUILT_RNCORE=0. On Android, set hermesV1Enabled=false in android/gradle.properties and configure the app to build React Native from source.

These methods ensure you can revert to the previous Hermes version if your app depends on behavior not supported in Hermes V1. Note that opting out may increase build times and reduce performance gains.

What Are Precompiled iOS Binaries and How Do They Reduce Build Times?

React Native 0.84 ships precompiled .xcframework binaries for iOS by default. This feature, previously opt-in, now automatically downloads and uses prebuilt React Native core libraries during pod install. You no longer need to compile React Native from source for every clean build, which dramatically cuts down build times.

This is especially beneficial for large projects or teams doing frequent builds. The precompiled binaries are platform-optimized and ready to use, so you can iterate faster.

If you need to compile from source—for example, to opt out of Hermes V1 or to include custom modifications—you can disable precompiled binaries by setting RCT_USE_PREBUILT_RNCORE=0 when installing pods. Otherwise, you enjoy faster builds with zero configuration.

Why Is React Native Removing Legacy Architecture Components?

React Native has been moving toward the New Architecture (Fabric and TurboModules) since version 0.68. Starting with 0.82, the New Architecture became the only runtime option. In 0.84, the team continues this cleanup by removing Legacy Architecture code from both iOS and Android. This follows the RFC that outlines incremental removals.

On iOS, an experimental flag RCT_REMOVE_LEGACY_ARCH was introduced in 0.83; now in 0.84 it is enabled by default. This means Legacy Architecture classes are no longer compiled into your iOS builds, reducing both build time and app size. No breakages are expected for apps already using the New Architecture—the codebase has been prepared to ensure compatibility.

The removal simplifies the framework, improves maintainability, and encourages migration for any apps still using the old architecture (though that’s rare since 0.82).

What Is the Minimum Node.js Version Required for React Native 0.84?

React Native 0.84 raises the minimum Node.js version to 22. This aligns with modern development practices and ensures you have the latest features and security updates. If your development environment uses an older Node.js version, you’ll need to upgrade to 22 or higher before installing this release.

Node.js 22 brings improved performance, better module system handling, and updated APIs. Upgrading is straightforward: you can use a version manager like nvm or fnm to switch, or download the latest installer from the official website.

Do I Need to Make Any Manual Changes to Migrate to React Native 0.84?

For most apps, migration is smooth. If you’re already using Hermes and the New Architecture (the default since 0.70 and 0.82 respectively), upgrading to 0.84 requires no manual configuration. The new defaults—Hermes V1, precompiled iOS binaries, and removal of legacy architecture—apply automatically.

However, if your app relies on any Legacy Architecture components (unlikely for recent versions), you should test thoroughly. Also, ensure your CI/environment uses Node.js 22+. If you encounter issues, consult the official upgrade guide and check for breaking changes specific to your libraries. The React Native team has designed this release to be a drop-in upgrade with immediate performance benefits.