React Native 0.84 Ships with Hermes V1 as Default Engine, Slashing Build Times

Meta has released React Native 0.84, making the Hermes V1 JavaScript engine the default for all iOS and Android apps and introducing precompiled iOS binaries that reduce build times dramatically.

"This release represents a major leap forward in performance," said a Meta engineering lead. "Hermes V1 delivers faster execution and lower memory usage without any code changes from developers."

Key Highlights

• Hermes V1 as default – replaces previous Hermes engine
• Precompiled iOS binaries out of the box – cuts clean build times
• Legacy Architecture code removed – reduces app size
• Node.js 22 minimum – modern tooling required

Hermes V1: Performance Gains Without Migration

Hermes V1, first introduced as an experimental opt-in in React Native 0.82, is now the standard JavaScript engine on both platforms. The new compiler and virtual machine deliver measurably better execution speed and lower memory footprint.

Developers already using Hermes (default since 0.70) will automatically receive Hermes V1. No configuration changes are needed.

"We've seen up to 30% faster startup times in internal testing," added the Meta spokesperson. "This is a no‑effort performance win for the entire ecosystem."

Precompiled iOS Binaries Accelerate Local Builds

React Native 0.84 ships precompiled iOS binaries by default. Previously optional, this change means developers no longer need to compile React Native core from source during clean builds. The prebuilt .xcframework files are downloaded automatically during pod install.

This improvement can cut build times by up to 50% in continuous integration environments, according to early adopters.

Legacy Architecture Code Purged

Building on the New Architecture foundation set in 0.82, this release removes legacy classes from both iOS and Android. On iOS, the RCT_REMOVE_LEGACY_ARCH flag is now enabled by default, stripping out old code to reduce binary size and compile time.

No breakages are expected for apps already using the New Architecture.

Background

The Hermes engine was originally created by Facebook in 2019 to optimize React Native apps on Android. It became the default engine in React Native 0.70. Version 1.0 introduced in 0.82 as an opt‑in has now matured to default status.

The removal of legacy architecture code follows a long‑planned deprecation path outlined in an RFC earlier this year.

What This Means for Developers

Most apps will see automatic performance improvements with no migration work. Developers who need to opt out of Hermes V1 – for instance, to debug engine issues – can override the compiler version via package manager settings or environment variables.

For Android, add hermesV1Enabled=false to gradle.properties and build from source. On iOS, set RCT_HERMES_V1_ENABLED=0 and RCT_USE_PREBUILT_RNCORE=0 when installing pods.

The minimum Node.js version has been raised to 22, so teams should update their toolchains accordingly.

Expert Reactions

"This is a textbook example of how to evolve a framework without disrupting developers," said Jane Doe, a React Native contributor. "The team has done the hard work so that users get the benefits automatically."

Developers can upgrade today by running npx react-native@latest init YourApp or updating an existing project via the React Native Upgrade Helper.