React Native 0.84: Hermes V1 Default, Faster Builds, and Cleaner Architecture
React Native 0.84 has arrived with several major improvements that streamline development and boost app performance. This update makes Hermes V1 the default JavaScript engine, introduces precompiled iOS binaries automatically, removes long-standing legacy architecture code, and raises the minimum Node.js requirement. Below, we answer the most pressing questions about this release.
What is the most significant change in React Native 0.84?
The headline feature is that Hermes V1 is now the default JavaScript engine for both iOS and Android. Following an experimental opt-in phase in version 0.82, Hermes V1 becomes the standard, delivering substantial performance improvements. This engine is a major upgrade from the previous Hermes version, with enhanced compiler and VM optimizations. Developers will see automatic gains in execution speed and memory usage without any configuration changes. This change builds on the fact that Hermes has been the default since React Native 0.70, so existing projects automatically upgrade to Hermes V1.
What performance benefits does Hermes V1 bring to my app?
Hermes V1 provides measurably better JavaScript performance through improvements in both its compiler and virtual machine. Apps will experience faster startup times, smoother runtime execution, and lower memory consumption. Because Hermes V1 is now the default, these benefits apply to all React Native apps automatically—no migration effort is required. If you were using Hermes before (which has been the default since 0.70), you simply get the upgraded engine for free. In benchmarks, the new engine shows notable reductions in parse and bytecode compilation times, leading to a snappier user experience.
How can I opt out of Hermes V1 and use the legacy version?
While Hermes V1 is the default, you can revert to the legacy hermes-compiler if needed. There are three methods depending on your platform and package manager:
- Package manager override: In your
package.json, add an override forhermes-compilerversion0.15.0. For npm use"overrides", for Yarn use"resolutions", and for pnpm use"pnpm": { "overrides": ... }. - iOS: When installing CocoaPods, set environment variables
RCT_HERMES_V1_ENABLED=0andRCT_USE_PREBUILT_RNCORE=0. - Android: Add
hermesV1Enabled=falsetoandroid/gradle.propertiesand configure the app to build React Native from source.
Note that opting out may require additional build steps and will lose the performance benefits of Hermes V1.
How do precompiled iOS binaries improve development?
React Native 0.84 ships precompiled iOS binaries by default, a feature that was previously opt-in. This means that when you run pod install, the prebuilt .xcframework binaries are automatically downloaded and linked—you no longer compile React Native core from source during a clean build. The result is significantly reduced build times for iOS apps. If you need to build from source (for example, because you opted out of Hermes V1), you can disable this feature by setting RCT_USE_PREBUILT_RNCORE=0 during pod installation.
What does the removal of Legacy Architecture mean for my project?
Continuing the transition started in React Native 0.82—which made the New Architecture the only runtime option—version 0.84 removes more Legacy Architecture classes from both iOS and Android. On iOS, the experimental RCT_REMOVE_LEGACY_ARCH flag is now enabled by default, stripping out legacy code from builds. This reduces build time and app size. Developers already using the New Architecture should experience no breakages; the legacy code is simply no longer included. The removal is part of an ongoing effort to clean up the codebase and simplify future development.
What are the system requirements for React Native 0.84?
React Native 0.84 now requires Node.js 22 or newer. This updated minimum ensures compatibility with the latest JavaScript features and tooling. If your development environment uses an older Node.js version, you will need to upgrade before installing this release. For most developers, upgrading Node.js is straightforward via version managers like nvm or fnm. This change aligns React Native with modern Node.js LTS releases and enables better performance and security.
Do I need to migrate my existing React Native project?
No manual migration is required for most projects. If you are already on React Native 0.70 or later (which defaults to Hermes), you will automatically receive Hermes V1 and the other improvements when you upgrade to 0.84. The only exception is if you have custom configurations that explicitly set a different JavaScript engine or build options. Always test your app after upgrading, but the team expects no breaking changes for apps already using the New Architecture. For detailed migration steps, refer to the official React Native upgrade helper.