Hermes is a JavaScript engine optimized for running React Native apps, focusing on fast startup using ahead-of-time static optimization and compact bytecode. It’s useful if you want to enable Hermes in a React Native project or build and integrate a custom Hermes build, with release notes aimed at specific React Native versions.
Project status
- Actively maintained: The repo has a very recent upstream push (2026-06-06), which suggests ongoing maintenance and development, even though the latest tagged public update shown here is older.
- Update cadence: The public version updates listed are sparse (v0.11.0 in 2022, v0.12.0 in 2022, v0.13.0 in 2024), indicating infrequent, larger updates rather than a steady cadence.
AI summary generated Today
Recent updates
v0.13.0
8/16/2024v0.13.0 release notes provide no functional change details beyond referencing React Native RN 0.75.0. The code diff shows substantial Hermes integration work, including a new async debugger API, modifications to DebuggerAPI internals, and significant changes to SynthTrace/SynthTrace parsing and error handling behavior.
Featuresv0.12.0
8/24/2022v0.12.0 is described as a large batch of bug fixes plus enabling WeakRef and BigInt support, with additional CLI performance improvements. The release notes also claim removal of the debugger from command line tools and that React Native now builds Hermes from source instead of requiring published Hermes binaries for specific RN targets.
BreakingFeaturesv0.11.0
1/27/2022Release v0.11.0 (for RN0.68.x) claims it is “in preparation for the 0.68.x” and focuses on Hermes bug fixes and performance improvements, but the release notes are otherwise non-specific. The code diff shows at least one new Hermes/JSI instrumentation facility plus significant build-flag controlled runtime lifecycle changes that are not described in the release notes.
v0.10.0
11/14/2021v0.10.0 is presented as an Hermes-focused update, intended to support the upcoming RN0.67 release. The release notes are high level and claim numerous bug fixes and performance improvements, but do not document specific API, build, or behavior changes.
v0.9.0
9/2/2021v0.9.0 is described as a Hermes update intended to close the gap before the React Native 0.66 cut, delivering memory and size wins plus bugfixes. The release notes are high-level and do not enumerate specific API, build, or behavioral changes.
Featuresv0.8.1
7/12/2021Hermes v0.8.1 prepares for the React Native 0.65 stable release with iOS build refinements for Apple Silicon (M1) simulators and Mac Catalyst, and introduces a directive intended to make Function.prototype.toString return original source. The code diff shows that the release actually implements a broader source visibility system (including additional directives), and adds a new function source table to the Hermes bytecode format. It also includes multiple undocumented build system and dependency changes, especially for Android and iOS packaging.
Featuresv0.8.0
4/29/2021Release v0.8.0 (RN 0.65.x release candidate) highlights Hermes runtime improvements: the new concurrent garbage collector "Hades" for shorter GC pauses, built-in Intl (ECMA-402) on Android by default, and additional memory and runtime performance fixes (including Function.prototype.toString behavior). The code diff provided, however, shows multiple significant API and tracing/instrumentation changes that are not mentioned in the release notes.
Featuresv0.7.2
12/9/2020v0.7.2 is described as a set of miscellaneous fixes to support the upgrade path to React Native 0.64. The code diff, however, shows substantial internal refactoring around tracing/trace parsing, plus build system and namespace changes (LLVM -> LLVH) that can impact downstream compilation and tooling consuming trace JSON.
Breakingv0.5.3
11/5/2020v0.5.3 is positioned as an update to provide macOS ARM64 support for Hermes on React Native (RN macOS v0.63.x). The release notes also state this version is Darwin-only (published as hermes-engine-darwin) and that non-Darwin users should use older versions.
BreakingFeaturesv0.7.1
10/10/2020Release v0.7.1 is described as an RN 0.64 pre-release for expanding Hermes support across more platforms via community PRs. The only documented distribution note is that, starting with this release, `hermes-runtime-darwin` will be published to the CocoaPod in place of `hermes-engine-darwin` to NPM.