React Native 0.84: Hermes V1 Takes Center Stage with Performance Gains and Faster Builds

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Introduction

React Native 0.84 has officially arrived, bringing a wave of improvements that streamline development and boost app performance. The standout change is the elevation of Hermes V1 to the default JavaScript engine on both iOS and Android, following its experimental introduction in version 0.82. This release also introduces precompiled iOS binaries by default, continues the removal of Legacy Architecture components, and raises the minimum Node.js requirement to 22. Together, these updates promise faster builds, leaner apps, and a more modern foundation for React Native projects.

React Native 0.84: Hermes V1 Takes Center Stage with Performance Gains and Faster Builds

Hermes V1 as the Default JavaScript Engine

Hermes V1 now powers React Native apps on both platforms by default. Building on the earlier Hermes engine that has been the default since version 0.70, this new iteration brings significant enhancements to the compiler and virtual machine, resulting in measurably better JavaScript performance.

What This Means for Your App

If you're already using Hermes, you'll automatically benefit from Hermes V1 without any configuration changes. The engine delivers automatic performance gains—improved execution speed and reduced memory usage—out of the box. No migration steps are required.

Opting out of Hermes V1

While Hermes V1 is now the standard, you can revert to the legacy engine if needed. Use your package manager to force installation of the older hermes-compiler package. For npm, add an override in package.json:

"overrides": { "hermes-compiler": "0.15.0" }

For Yarn (v1), use a resolutions field:

"resolutions": { "hermes-compiler": "0.15.0" }

For pnpm, set:

"pnpm": { "overrides": { "hermes-compiler": "0.15.0" } }

On iOS, during CocoaPods installation, pass environment variables:

RCT_HERMES_V1_ENABLED=0 RCT_USE_PREBUILT_RNCORE=0 pod install

On Android, add to android/gradle.properties:

hermesV1Enabled=false

Then configure the app to build React Native from source.

Precompiled Binaries on iOS by Default

Starting with React Native 0.84, iOS builds ship precompiled binaries by default. Previously an opt-in feature, this change eliminates the need to compile React Native core from source during every clean build. The precompiled .xcframework binaries are automatically downloaded and used when you run pod install, dramatically reducing build times.

If your project requires building from source—for example, when opting out of Hermes V1—you can disable precompiled binaries by setting RCT_USE_PREBUILT_RNCORE=0 before installing pods.

Legacy Architecture Components Removed

React Native 0.84 continues the cleanup of Legacy Architecture code that began in version 0.82. With the New Architecture now the only runtime option, the team is systematically removing legacy classes on both platforms, as outlined in the RFC.

iOS

In version 0.83, the experimental flag RCT_REMOVE_LEGACY_ARCH allowed compilation without Legacy Architecture code. In 0.84, this behavior is the default—Legacy Architecture components are no longer included in iOS builds. This reduces both build time and app size, with no expected breakages for apps already running on the New Architecture.

Android

Similar removals are taking place on Android, though the exact classes being dropped are detailed in the release notes. Developers are advised to ensure their custom native modules and components are fully migrated to the New Architecture to avoid issues.

Node.js 22 Minimum Requirement

React Native 0.84 now requires Node.js 22 as the minimum version. This aligns with the latest stable Node.js release and enables use of modern JavaScript features and improved tooling. If your development environment uses an older Node.js version, upgrade before installing this React Native release.

Summary of Key Benefits

Automatic performance improvements through Hermes V1’s enhanced compiler and VM.
Faster iOS builds thanks to precompiled binaries as the default.
Smaller app size due to removal of Legacy Architecture code.
Simpler development workflow with no migration effort for most projects.

React Native 0.84 represents a mature, performance-focused release that solidifies the New Architecture as the standard. Whether you’re building a new app or upgrading an existing one, these changes provide a smoother, faster experience. For full details, see the official release notes.

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