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

[cipolleschi]

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:

1. Run bundle exec pod install and verified that Hermes V1 is used when building from source

2. Run `prebuild-ios -s` and verified that the scripts downloads the Hermes V1 tarball 3. GHA and nightlies

[meta-codesync]

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

[github-actions]

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]

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]

@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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

This pull request was successfully merged by @cipolleschi in f140c49

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