React Native 0.84 Delivers Major Performance Boost with Hermes V1 as Default Engine

Revolutionizing React Native Performance with Hermes V1

React Native 0.84 has arrived, marking a pivotal moment for mobile app development. This release elevates the Hermes V1 JavaScript engine to default status on both iOS and Android, delivering automatic performance gains across the board. Additionally, it streamlines build processes with precompiled iOS binaries and continues the systematic removal of legacy architecture components. Let’s explore what these changes mean for your development workflow and your apps.

Hermes V1 Becomes the Default JavaScript Engine

After its experimental introduction in React Native 0.82, Hermes V1 is now the standard JavaScript engine for all new and existing React Native projects. This next-generation engine features a refined compiler and virtual machine that translate into measurable improvements in execution speed and memory usage. For developers, this means your apps will automatically benefit from smoother performance and reduced resource consumption—no extra configuration required.

Seamless Migration for Existing Users

If your project already uses Hermes (which has been the default since version 0.70), upgrading to React Native 0.84 will automatically switch to Hermes V1. You don’t need to modify any configuration files or update dependencies. The transition is transparent, and your app will start using the improved engine with zero effort on your part.

Opting Out of Hermes V1

While Hermes V1 is the recommended choice for most projects, some advanced use cases or compatibility requirements may necessitate reverting to the legacy Hermes compiler. Here’s how to opt out on each platform:

Using Package Manager Overrides

Force the installation of the legacy hermes-compiler package by adding overrides to your package.json:

• npm: "overrides": { "hermes-compiler": "0.15.0" }
• yarn: "resolutions": { "hermes-compiler": "0.15.0" }
• pnpm: "pnpm": { "overrides": { "hermes-compiler": "0.15.0" } }

On iOS

When installing CocoaPods dependencies, set the environment variables RCT_HERMES_V1_ENABLED=0 and RCT_USE_PREBUILT_RNCORE=0.

On Android

Add hermesV1Enabled=false in android/gradle.properties and configure your application to build React Native from source.

Precompiled iOS Binaries Now Standard

React Native 0.84 introduces precompiled iOS binaries as the default, a feature that was previously opt-in. Instead of compiling React Native core from source during each clean build, the precompiled .xcframework binaries are now automatically downloaded and used during pod install. This change dramatically reduces iOS build times, allowing developers to iterate faster.

Disabling Precompiled Binaries

If you need to build React Native from source—for example, to opt out of Hermes V1 or for custom modifications—you can disable this feature by setting RCT_USE_PREBUILT_RNCORE=0 when installing pods.

Continued Removal of Legacy Architecture

React Native 0.82 made the New Architecture the only runtime option. Now with version 0.84, the team continues to prune legacy architecture code from both iOS and Android platforms, as outlined in the RFC.

iOS Changes

In version 0.83, the experimental RCT_REMOVE_LEGACY_ARCH flag was introduced to compile out legacy code. With 0.84, this behavior is now the default. As a result, legacy architecture code is no longer included in iOS builds, leading to:

• Faster build times – Less code to compile means shorter build cycles.
• Smaller app size – Unused legacy code is omitted from the final binary.

For apps already running on the New Architecture, no breakages are expected. This change solidifies the foundation for a leaner, more efficient React Native.

Updated System Requirements: Node.js 22 Minimum

React Native 0.84 now requires Node.js version 22 or higher. This aligns the framework with the latest LTS releases and ensures compatibility with modern tooling and performance optimizations. Before upgrading, verify your development environment meets this requirement to avoid build issues.

Conclusion: A Leaner, Faster React Native

React Native 0.84 represents a significant step forward in performance and developer experience. With Hermes V1 as the default JavaScript engine, precompiled iOS binaries slashing build times, and the removal of legacy architecture reducing bloat, this release empowers developers to create faster, smaller apps with less effort. Upgrade today and take advantage of these enhancements—your apps will thank you.