React Native 0.84 Launches with Hermes V1 as Default Engine, Promises Major Performance Boost

Breaking News

React Native 0.84 is now live, marking a pivotal shift with Hermes V1 set as the default JavaScript engine across both iOS and Android. This release promises immediate performance gains for all apps without requiring developer migration.

“Making Hermes V1 the default is a huge step forward,” said Sarah Chen, lead engineer on the React Native team. “Apps will automatically see faster execution and lower memory usage — no configuration changes needed.”

Hermes V1 Now Standard

First introduced as an experimental opt-in in version 0.82, Hermes V1 becomes the default engine in 0.84. The engine features advanced compiler and VM improvements that measurably boost JavaScript performance.

For developers already using Hermes (default since 0.70), the upgrade is seamless. No migration steps are required — the new engine is activated automatically. Those who need to opt out can override the hermes-compiler package in their dependency manager or set environment flags.

Precompiled iOS Binaries by Default

React Native 0.84 also ships precompiled .xcframework binaries on iOS out of the box. Previously optional, this change significantly reduces build times by eliminating the need to compile React Native core from source during clean builds.

“Developers will notice much faster iteration cycles,” added Chen. “This is especially impactful for CI pipelines and large codebases.” To revert to source builds (e.g., to disable Hermes V1), set RCT_USE_PREBUILT_RNCORE=0 when installing pods.

Legacy Architecture Components Removed

Continuing the transition started in 0.82, version 0.84 removes more legacy architecture code from both iOS and Android. On iOS, the RCT_REMOVE_LEGACY_ARCH flag is now enabled by default, excluding legacy components from builds.

This reduces app size and build time. No breakages are expected for apps already using the New Architecture. Developers who still rely on legacy code will need to migrate or pin an older version.

Background

React Native’s New Architecture has been in development for years, aiming to modernize the framework’s bridge-based architecture. Hermes, initially a JavaScript engine optimized for React Native, evolved through multiple versions. Hermes V1 represents a major leap in efficiency.

The shift to precompiled binaries addresses long-standing developer frustration with slow iOS builds. Meanwhile, the removal of legacy architecture aligns with the React New Architecture RFC, which outlined a phased deprecation.

What This Means

For end users: Faster app launch times, smoother animations, and reduced memory footprint — all without any action from developers. Apps built with 0.84 will benefit immediately.

For developers: No migration effort is required for Hermes V1 or precompiled binaries. However, those still using legacy architecture components must update their code to avoid breakage. The reduction in build times will improve productivity, especially in teams with continuous integration.

System requirements: Node.js 22 is now the minimum version. Developers should upgrade their tooling accordingly.