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The Wire · Showcase

REACT NATIVE KILLS FABRIC FEATURE FLAGS, JEST ADDS CONDITIONAL MOCKS

By RepoJournal · Filed · About Meta

React Native is shipping Fabric by default after ripping out the last feature flags that controlled the new architecture rollout.

The team completed a multi-PR teardown of the Fabric renderer flags [1][2][3]. The `fixFindShadowNodeByTagRaceCondition` flag is gone [1], replaced with permanent bug fixes for a use-after-free in shadow node lookup. Two more Fabric gates were deleted [2][3], collapsing conditional logic since `enableFabricRenderer()` always returned true on canary anyway. This means Fabric is now the only path for new architecture apps. On the Android side, React Native bumped Kotlin from 1.9 to 2.0 [4] because newer Kotlin versions deprecated older API levels and broke builds with -Werror. Jest shipped a major mock improvement: `mockFn.whenCalledWith(...args)` [5] finally lets you configure return values per argument without branching inside `mockImplementation`. The team also added a pluggable `haste.backend` config option [6], seeding support for Parcel's file watcher in future releases. A behavioral refactor [7] split the 1,157-line `HasteMap` godclass into multiple files, laying groundwork for that watcher swap.

Action items

References

  1. [1] Remove `fixFindShadowNodeByTagRaceCondition` feature flag (#56850) facebook/react-native
  2. [2] Remove enableFabricRenderer() call from InteropModuleRegistry (#56852) facebook/react-native
  3. [3] Remove enableFabricRenderer() call from UIManagerModuleConstantsHelper (#56851) facebook/react-native
  4. [4] Bump Kotlin API version from 1.9 to 2.0 (#56849) facebook/react-native
  5. [5] feat(jest-mock): add `mock.whenCalledWith(...)` ↗ facebook/jest
  6. [6] feat(haste-map): add `haste.backend` option ↗ facebook/jest
  7. [7] chore(haste-map): refactor massive class into multiple files ↗ facebook/jest

FAQ

What changed in Meta on May 16, 2026?
React Native is shipping Fabric by default after ripping out the last feature flags that controlled the new architecture rollout.
What should Meta teams do about it?
Audit React Native apps for remaining Fabric feature flags and remove conditional logic • If using React Native on Android, bump Kotlin to 2.0 or higher in your build config • Test Jest mock changes with existing `mockImplementation` tests before upgrading
Which Meta repositories shipped on May 16, 2026?
facebook/react-native, facebook/jest

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