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[RN][iOS][HermesV1] Use Hermes V1 as default engine #54989

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[RN][iOS][HermesV1] Use Hermes V1 as default engine #54989

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@cipolleschi cipolleschi commented Dec 29, 2025 •
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Summary:

This change makes Hermes V1 the default engine for React Native for iOS. This change needs to land before the branch cut of react native 0.84

Changelog:

[iOS][Changed] - Make Hermes V1 the default engine for iOS

Test Plan:

  1. Run bundle exec pod install and verified that Hermes V1 is used when building from source
Simulator Screenshot - iPhone 17 Pro - 2025-12-29 at 11 28 44 2. Run `prebuild-ios -s` and verified that the scripts downloads the Hermes V1 tarball Screenshot 2025-12-29 at 10 37 53 3. GHA and nightlies
@meta-cla meta-cla bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Dec 29, 2025
@cipolleschi cipolleschi changed the title [RN][HermesV1] Use Hermes V1 as default engine Dec 29, 2025
@cipolleschi cipolleschi marked this pull request as ready for review December 29, 2025 09:50
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meta-codesync bot commented Dec 29, 2025

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this in D89881943.
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github-actions bot commented Dec 29, 2025

Job Summary for Gradle

Test All :: build_android
Gradle Root Project Requested Tasks Gradle Version Build Outcome Build Scan®
react-native-github publishAllToMavenTempLocal build 9.0.0 ❌ Build Scan not published
@cipolleschi cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch 2 times, most recently from 0da20c6 to 5064dfa Compare December 29, 2025 14:14
@cipolleschi cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from 5064dfa to 350a654 Compare December 29, 2025 14:15
@complexapps2026
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complexapps2026 commented Dec 29, 2025

I’m pretty new to React Native and this change for iOS looks great. Could you help me understand if Android will use Hermes V1 by default too?
@cipolleschi
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cipolleschi commented Dec 29, 2025

@complexapps2026 the goal is also for Android to do that. this PR only contains changes related to iOS. A similar PR for Android will be opened soon!
@cipolleschi cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from 30b8850 to 473d292 Compare December 29, 2025 16:56
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@cipolleschi @complexapps2026 @facebook-github-bot