[RN][HermesV1] Use Hermes V1 as default engine by cipolleschi · Pull Request #54989 · react/react-native

cipolleschi · 2025-12-29T09:48:53Z

Summary:

This change makes Hermes V1 the default engine for React Native for both platforms. 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:

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

3. GHA and nightlies

meta-codesync · 2025-12-29T09:51:44Z

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this in D89881943.

github-actions · 2025-12-29T10:42:29Z

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	❌

complexapps2026 · 2025-12-29T15:42:28Z

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 · 2025-12-29T16:55:54Z

@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!

github-actions · 2026-01-06T12:36:47Z

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

github-actions · 2026-01-06T12:37:04Z

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	❌

github-actions · 2026-01-06T13:31:50Z

Job Summary for Gradle

Test All :: run_fantom_tests

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react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

github-actions · 2026-01-06T13:32:05Z

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	❌

github-actions · 2026-01-06T13:36:15Z

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

github-actions · 2026-01-06T14:03:24Z

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	❌

github-actions · 2026-01-06T17:37:39Z

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

github-actions · 2026-01-06T18:03:40Z

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	❌

github-actions · 2026-01-06T18:16:12Z

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

github-actions · 2026-01-07T10:01:24Z

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌

cortinico

Review automatically exported from Phabricator review in Meta.

react-native-bot · 2026-01-07T13:36:32Z

This pull request was successfully merged by @cipolleschi in f140c49

^{When will my fix make it into a release? | How to file a pick request?}

Summary: This change makes Hermes V1 the default engine for React Native for both platforms. This change needs to land before the branch cut of react native 0.84 bypass-github-export-checks ## Changelog: [iOS][Changed] - Make Hermes V1 the default engine for iOS Pull Request resolved: #54989 Test Plan: 1. Run `bundle exec pod install` and verified that Hermes V1 is used when building from source <img height="480" alt="Simulator Screenshot - iPhone 17 Pro - 2025-12-29 at 11 28 44" src="https://github.com/user-attachments/assets/0889f16c-f2ee-4a0e-9a4d-529dd82c8283" /> 2. Run `prebuild-ios -s` and verified that the scripts downloads the Hermes V1 tarball <img width="831" height="324" alt="Screenshot 2025-12-29 at 10 37 53" src="https://github.com/user-attachments/assets/9a60565e-1e13-4967-a4a4-dd079e6b040f" /> 3. GHA and nightlies Reviewed By: vzaidman, cortinico, huntie Differential Revision: D89881943 Pulled By: cipolleschi fbshipit-source-id: 958b6d31bd4230ba4a5c7fee2bffc19e03dcbc89

react-native-bot · 2026-01-12T16:26:47Z

This pull request was successfully merged by @cipolleschi in bbe02de

^{When will my fix make it into a release? | How to file a pick request?}

hannojg · 2026-01-15T15:49:21Z

Hey, this seems to have broken the fantom tests:

https://github.com/facebook/react-native/actions/runs/20783304330

cortinico · 2026-01-15T17:07:42Z

Yeah we're aware of it @hannojg

Summary: Changing the line in `ReactPlugin.kt` that always set `hermesV1Enabled` to `true` even if it was explicitly disabled, accidentally omitted in #54989. In recent update of hermes V1 binary a file `RuntimeAdapter.h` was removed. ## Changelog: [ANDROID] [FIXED] - ReactPlugin.kt always setting `hermesV1Enabled` to `true` Pull Request resolved: #55399 Test Plan: Build React Native from source on latest 0.84 RC, disable hermesV1 and see that it compiles now. Reviewed By: cipolleschi Differential Revision: D92267385 Pulled By: cortinico fbshipit-source-id: 58ecae6d3064995ef9e63ddbd67ac04db2a1126b

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

facebook-github-bot added p: Facebook Partner: Facebook Partner labels Dec 29, 2025

cipolleschi changed the title ~~[RN][HermesV1] Use Hermes V1 as default engine~~ [RN][iOS][HermesV1] Use Hermes V1 as default engine Dec 29, 2025

cipolleschi marked this pull request as ready for review December 29, 2025 09:50

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch 3 times, most recently from 5064dfa to 350a654 Compare December 29, 2025 14:15

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch 2 times, most recently from 4faf893 to d88d553 Compare January 5, 2026 13:50

cipolleschi mentioned this pull request Jan 5, 2026

Enable hermesV1Enabled=true by default on Android #55040

Closed

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from d88d553 to b42ebc6 Compare January 5, 2026 16:57

cipolleschi added 8 commits January 6, 2026 10:04

[RN][HermesV1] Use Hermes V1 as default engine

8b1257b

Make sure we can use Hermes V1 from RNTester

63f88e9

fix builds for SwiftPM and address comments on diff

76e72d1

address nits

a309998

fix version of Hermes in CI

5b9cee0

Fix setup for hermes in CI

27d7278

Fix HermesV1 build from source in CI

3162f07

put HERMES_ENABLE_DEBUGGER back

874f569

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from b42ebc6 to 874f569 Compare January 6, 2026 10:05

cipolleschi changed the title ~~[RN][iOS][HermesV1] Use Hermes V1 as default engine~~ [RN][HermesV1] Use Hermes V1 as default engine Jan 6, 2026

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch 2 times, most recently from eb1669e to e99a190 Compare January 6, 2026 13:31

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from e99a190 to 9eddb95 Compare January 6, 2026 17:32

[Android] bring in android changes

fcdd1a0

cipolleschi force-pushed the cipolleschi/enable-hermes-v1-by-default branch from 9eddb95 to fcdd1a0 Compare January 6, 2026 18:11

cortinico approved these changes Jan 7, 2026

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meta-codesync Bot closed this in f140c49 Jan 7, 2026

react-native-bot added the Merged This PR has been merged. label Jan 7, 2026

cortinico mentioned this pull request Jan 7, 2026

[0.84] Use Hermes V1 as default on Android/iOS reactwg/react-native-releases#1202

Closed

This was referenced Jan 13, 2026

[LOCAL][RN][iOS] Fix CI iOS jobs failing because of RCTTestRunner not found #55141

Merged

[LOCAL][RN][IOS] Fix Template E2E tests #55142

Merged

tjzel mentioned this pull request Feb 3, 2026

fix: inability to disable hermesV1 on Android #55399

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