Using Hermes Engine
Hermes is currently only supported for Android apps using SDK 42 or higher, built with EAS Build
. There are no plans to backport support to
. Jump to "Limitations"
To get started, open your
app.json and add
jsEngine field under the
Now you can build an APK or AAB through
Publishing updates with both
expo publish and
expo export will generate Hermes bytecode bundles and their sourcemaps.
Please note that the Hermes bytecode format may change between different versions of
— an update produced for a specific version of Hermes will not run on a different version of Hermes. Updating the Hermes version can be thought of in the same way as updating any other native module, and so if you update the
version you should also update the
. If you don't do this, your app may crash on launch because the update may be loaded by an existing binary that uses an older version of
that is incompatible with the updated bytecode format. See "Update Compatibility"
for more information.
- This is only supported on a debug build app.
expo start and make sure Expo development server is running.
iOS is not supported yet — Hermes support was added to React Native for iOS in
firstname.lastname@example.org and will likely to be added to Expo projects when it has been used successfully in production more broadly.
The classic build system isn't flexible enough
to support using Hermes for some apps and not for others. You will need to use the new build system, EAS Build
, to use Hermes in your standalone apps.