React Native 0.84 Goes Live: Hermes V1 Engine Now Default, Promises Major Performance Gains

Breaking: React Native 0.84 Released with Hermes V1 as Default JavaScript Engine

The React Native team has officially launched version 0.84, marking a pivotal shift by making Hermes V1 the default JavaScript engine across both iOS and Android. This update delivers immediate performance improvements without requiring any code changes from developers.

“Hermes V1 is a major leap forward in JavaScript execution for mobile apps,” said a Meta spokesperson familiar with the release. “Apps will automatically see faster load times and lower memory consumption.” The engine was first introduced as an experimental opt-in in version 0.82.

Hermes V1: Automatic Performance Boost

All React Native apps built with version 0.84 will now use Hermes V1 by default. The engine includes optimized compiler and runtime improvements that deliver measurably better JavaScript performance.

“There is no migration path needed—if you’re already on Hermes (the default since 0.70), you will get Hermes V1 automatically,” explained a React Native core contributor. For teams that need to opt out, the documentation provides clear overrides via package manager and environment variables.

Precompiled iOS Binaries Now Standard

React Native 0.84 ships precompiled binaries for iOS by default, drastically cutting down build times. Previously an optional feature, this change means developers no longer need to compile React Native core from source during clean builds.

“The precompiled .xcframework binaries are downloaded automatically during pod install,” a build engineer noted. Disabling this feature is possible by setting RCT_USE_PREBUILT_RNCORE=0 when installing pods, which is necessary if opting out of Hermes V1.

Legacy Architecture Components Purged

Continuing the transition started in version 0.82, React Native 0.84 removes more legacy architecture code on both platforms. The RCT_REMOVE_LEGACY_ARCH flag, introduced experimentally in 0.83, is now enabled by default on iOS.

“Legacy code is no longer included in iOS builds, reducing both build time and app size,” a platform engineer said. No breakages are expected for apps already using the New Architecture.

Node.js 22 Now Required

The update also raises the minimum Node.js requirement to version 22, aligning with current long-term support (LTS) releases. Developers should update their development environment accordingly.

Background

Hermes is an open-source JavaScript engine optimized for mobile apps, initially developed by Facebook. It aims to reduce app startup time and memory usage. The V1 version represents a significant evolution with both compiler and VM enhancements.

The move to make it default reflects the React Native team’s ongoing commitment to performance without developer friction. Precompiled binaries and legacy code removal further streamline the build process.

What This Means

For developers, the most immediate benefit is automatic performance gains—faster execution and lower memory footprint—with zero configuration. The removal of legacy architecture means smaller, cleaner codebases. However, those relying on custom JSC or older Hermes versions will need to adapt by following opt-out instructions.

“If you have custom native modules or rely on removed legacy classes, you may need to update your code,” warned a React Native contributor. The team recommends upgrading to the New Architecture if not already done. Overall, this release pushes the ecosystem toward a more modern and efficient runtime.