diff --git a/packages/react-dom-bindings/src/client/validateDOMNesting.js b/packages/react-dom-bindings/src/client/validateDOMNesting.js
index 49d8b5c158f62..d6fdc5e857ed3 100644
--- a/packages/react-dom-bindings/src/client/validateDOMNesting.js
+++ b/packages/react-dom-bindings/src/client/validateDOMNesting.js
@@ -297,6 +297,8 @@ function isTagValidWithParent(tag: string, parentTag: ?string): boolean {
         tag === 'hr' ||
         tag === 'option' ||
         tag === 'optgroup' ||
+        tag === 'script' ||
+        tag === 'template' ||
         tag === '#text'
       );
     case 'optgroup':
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 632b2df70c097..71affb7ca7a44 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -92,7 +92,6 @@ import {
   DidDefer,
 } from './ReactFiberFlags';
 import {
-  debugRenderPhaseSideEffectsForStrictMode,
   disableLegacyContext,
   disableLegacyContextForFunctionComponents,
   enableProfilerCommitHooks,
@@ -1375,10 +1374,7 @@ function finishClassComponent(
     }
     if (__DEV__) {
       nextChildren = callRenderInDEV(instance);
-      if (
-        debugRenderPhaseSideEffectsForStrictMode &&
-        workInProgress.mode & StrictLegacyMode
-      ) {
+      if (workInProgress.mode & StrictLegacyMode) {
         setIsStrictModeForDevtools(true);
         try {
           callRenderInDEV(instance);
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.js b/packages/react-reconciler/src/ReactFiberClassComponent.js
index 7ebf0fb9f4b92..d0490b7e02d4e 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.js
@@ -18,7 +18,6 @@ import {
   MountLayoutDev,
 } from './ReactFiberFlags';
 import {
-  debugRenderPhaseSideEffectsForStrictMode,
   disableLegacyContext,
   enableSchedulingProfiler,
   disableDefaultPropsExceptForClasses,
@@ -138,10 +137,7 @@ function applyDerivedStateFromProps(
   const prevState = workInProgress.memoizedState;
   let partialState = getDerivedStateFromProps(nextProps, prevState);
   if (__DEV__) {
-    if (
-      debugRenderPhaseSideEffectsForStrictMode &&
-      workInProgress.mode & StrictLegacyMode
-    ) {
+    if (workInProgress.mode & StrictLegacyMode) {
       setIsStrictModeForDevtools(true);
       try {
         // Invoke the function an extra time to help detect side-effects.
@@ -266,10 +262,7 @@ function checkShouldComponentUpdate(
       nextContext,
     );
     if (__DEV__) {
-      if (
-        debugRenderPhaseSideEffectsForStrictMode &&
-        workInProgress.mode & StrictLegacyMode
-      ) {
+      if (workInProgress.mode & StrictLegacyMode) {
         setIsStrictModeForDevtools(true);
         try {
           // Invoke the function an extra time to help detect side-effects.
@@ -598,10 +591,7 @@ function constructClassInstance(
   let instance = new ctor(props, context);
   // Instantiate twice to help detect side-effects.
   if (__DEV__) {
-    if (
-      debugRenderPhaseSideEffectsForStrictMode &&
-      workInProgress.mode & StrictLegacyMode
-    ) {
+    if (workInProgress.mode & StrictLegacyMode) {
       setIsStrictModeForDevtools(true);
       try {
         instance = new ctor(props, context);
diff --git a/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js b/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
index 7945e4fb1c915..23bef1e6b0983 100644
--- a/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
+++ b/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
@@ -110,8 +110,6 @@ import {
 } from './ReactFiberFlags';
 import getComponentNameFromFiber from './getComponentNameFromFiber';
 
-import {debugRenderPhaseSideEffectsForStrictMode} from 'shared/ReactFeatureFlags';
-
 import {StrictLegacyMode} from './ReactTypeOfMode';
 import {
   markSkippedUpdateLanes,
@@ -402,10 +400,7 @@ function getStateFromUpdate<State>(
         }
         const nextState = payload.call(instance, prevState, nextProps);
         if (__DEV__) {
-          if (
-            debugRenderPhaseSideEffectsForStrictMode &&
-            workInProgress.mode & StrictLegacyMode
-          ) {
+          if (workInProgress.mode & StrictLegacyMode) {
             setIsStrictModeForDevtools(true);
             try {
               payload.call(instance, prevState, nextProps);
@@ -435,10 +430,7 @@ function getStateFromUpdate<State>(
         }
         partialState = payload.call(instance, prevState, nextProps);
         if (__DEV__) {
-          if (
-            debugRenderPhaseSideEffectsForStrictMode &&
-            workInProgress.mode & StrictLegacyMode
-          ) {
+          if (workInProgress.mode & StrictLegacyMode) {
             setIsStrictModeForDevtools(true);
             try {
               payload.call(instance, prevState, nextProps);
diff --git a/packages/react-reconciler/src/ReactFiberHooks.js b/packages/react-reconciler/src/ReactFiberHooks.js
index 99dbea044690f..e76b78b2ce2a8 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.js
@@ -40,7 +40,6 @@ import {
   enableUseEffectEventHook,
   enableUseResourceEffectHook,
   enableLegacyCache,
-  debugRenderPhaseSideEffectsForStrictMode,
   disableLegacyMode,
   enableNoCloningMemoCache,
 } from 'shared/ReactFeatureFlags';
@@ -623,9 +622,7 @@ export function renderWithHooks<Props, SecondArg>(
   //
   // There are plenty of tests to ensure this behavior is correct.
   const shouldDoubleRenderDEV =
-    __DEV__ &&
-    debugRenderPhaseSideEffectsForStrictMode &&
-    (workInProgress.mode & StrictLegacyMode) !== NoMode;
+    __DEV__ && (workInProgress.mode & StrictLegacyMode) !== NoMode;
 
   shouldDoubleInvokeUserFnsInHooksDEV = shouldDoubleRenderDEV;
   let children = __DEV__
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.js b/packages/react-reconciler/src/ReactFiberWorkLoop.js
index a71eb543cfe5d..7377f605a8811 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.js
@@ -32,7 +32,6 @@ import {
   enableSchedulingProfiler,
   enableUpdaterTracking,
   enableTransitionTracing,
-  useModernStrictMode,
   disableLegacyContext,
   alwaysThrottleRetries,
   enableInfiniteRenderLoopDetection,
@@ -4205,7 +4204,7 @@ function commitDoubleInvokeEffectsInDEV(
   hasPassiveEffects: boolean,
 ) {
   if (__DEV__) {
-    if (useModernStrictMode && (disableLegacyMode || root.tag !== LegacyRoot)) {
+    if (disableLegacyMode || root.tag !== LegacyRoot) {
       let doubleInvokeEffects = true;
 
       if (
diff --git a/packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js b/packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js
index 85365d3e708fc..12b319080de5c 100644
--- a/packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js
+++ b/packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js
@@ -77,7 +77,7 @@ describe('Activity StrictMode', () => {
     ]);
   });
 
-  // @gate __DEV__ && enableActivity && useModernStrictMode
+  // @gate __DEV__ && enableActivity
   it('should not trigger strict effects when offscreen is hidden', async () => {
     await act(() => {
       ReactNoop.render(
diff --git a/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js b/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
index 556e0559728e7..8b0e903a839e9 100644
--- a/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
@@ -13,7 +13,6 @@
 'use strict';
 
 let React;
-let ReactFeatureFlags;
 let ReactTestRenderer;
 let Scheduler;
 let ReactDOMServer;
@@ -26,8 +25,6 @@ let waitForThrow;
 describe('ReactHooks', () => {
   beforeEach(() => {
     jest.resetModules();
-    ReactFeatureFlags = require('shared/ReactFeatureFlags');
-
     React = require('react');
     ReactTestRenderer = require('react-test-renderer');
     Scheduler = require('scheduler');
@@ -1240,8 +1237,6 @@ describe('ReactHooks', () => {
   });
 
   it('double-invokes components with Hooks in Strict Mode', async () => {
-    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = true;
-
     const {useState, StrictMode} = React;
     let renderCount = 0;
 
@@ -1459,7 +1454,6 @@ describe('ReactHooks', () => {
   });
 
   it('double-invokes useMemo in DEV StrictMode despite []', async () => {
-    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = true;
     const {useMemo, StrictMode} = React;
 
     let useMemoCount = 0;
diff --git a/packages/react-reconciler/src/__tests__/ReactUpdaters-test.internal.js b/packages/react-reconciler/src/__tests__/ReactUpdaters-test.internal.js
index 3f7fcd28aec3d..3aa76b0c2ddfa 100644
--- a/packages/react-reconciler/src/__tests__/ReactUpdaters-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactUpdaters-test.internal.js
@@ -34,7 +34,6 @@ describe('updaters', () => {
 
     ReactFeatureFlags = require('shared/ReactFeatureFlags');
     ReactFeatureFlags.enableUpdaterTracking = true;
-    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = false;
 
     mockDevToolsHook = {
       injectInternals: jest.fn(() => {}),
diff --git a/packages/react-reconciler/src/__tests__/StrictEffectsMode-test.js b/packages/react-reconciler/src/__tests__/StrictEffectsMode-test.js
index 0ce01a650c323..0c7e75c39a4a5 100644
--- a/packages/react-reconciler/src/__tests__/StrictEffectsMode-test.js
+++ b/packages/react-reconciler/src/__tests__/StrictEffectsMode-test.js
@@ -945,34 +945,25 @@ describe('StrictEffectsMode', () => {
       shouldSuspend = false;
     });
 
-    if (gate(flags => flags.useModernStrictMode)) {
-      expect(log).toEqual([
-        'Child rendered',
-        'Child rendered',
-        // !!! Committed, destroy and create effect.
-        // !!! The other effect is not destroyed and created
-        // !!! because the dep didn't change
-        'Child dep destroy',
-        'Child dep create',
-
-        // Double invoke both effects
-        'Child destroy',
-        'Child dep destroy',
-        'Child create',
-        'Child dep create',
-        // Fires setState
-        '-----------------------after setState',
-        'Child rendered',
-        'Child rendered',
-        'Child dep create',
-      ]);
-    } else {
-      expect(log).toEqual([
-        'Child rendered',
-        'Child rendered',
-        'Child dep destroy',
-        'Child dep create',
-      ]);
-    }
+    expect(log).toEqual([
+      'Child rendered',
+      'Child rendered',
+      // !!! Committed, destroy and create effect.
+      // !!! The other effect is not destroyed and created
+      // !!! because the dep didn't change
+      'Child dep destroy',
+      'Child dep create',
+
+      // Double invoke both effects
+      'Child destroy',
+      'Child dep destroy',
+      'Child create',
+      'Child dep create',
+      // Fires setState
+      '-----------------------after setState',
+      'Child rendered',
+      'Child rendered',
+      'Child dep create',
+    ]);
   });
 });
diff --git a/packages/react-reconciler/src/__tests__/StrictEffectsModeDefaults-test.internal.js b/packages/react-reconciler/src/__tests__/StrictEffectsModeDefaults-test.internal.js
index c9f65a20a0c7b..5829cd0904266 100644
--- a/packages/react-reconciler/src/__tests__/StrictEffectsModeDefaults-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/StrictEffectsModeDefaults-test.internal.js
@@ -461,7 +461,6 @@ describe('StrictEffectsMode defaults', () => {
       expect(log).toEqual([]);
     });
 
-    //@gate useModernStrictMode
     it('disconnects refs during double invoking', async () => {
       const onRefMock = jest.fn();
       function App({text}) {
diff --git a/packages/react-reconciler/src/__tests__/useRef-test.internal.js b/packages/react-reconciler/src/__tests__/useRef-test.internal.js
index 19a8d29211df0..2a6ab6ab58cca 100644
--- a/packages/react-reconciler/src/__tests__/useRef-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/useRef-test.internal.js
@@ -28,9 +28,6 @@ describe('useRef', () => {
     ReactNoop = require('react-noop-renderer');
     Scheduler = require('scheduler');
 
-    const ReactFeatureFlags = require('shared/ReactFeatureFlags');
-    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = false;
-
     act = require('internal-test-utils').act;
     useCallback = React.useCallback;
     useEffect = React.useEffect;
diff --git a/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMReplyEdge-test.js b/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMReplyEdge-test.js
index 0c6ec9599e1e2..f6157dff171d7 100644
--- a/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMReplyEdge-test.js
+++ b/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMReplyEdge-test.js
@@ -245,4 +245,31 @@ describe('ReactFlightDOMReplyEdge', () => {
       ),
     );
   });
+
+  it('should abort when parsing an incomplete payload', async () => {
+    const infinitePromise = new Promise(() => {});
+    const controller = new AbortController();
+    const promiseForResult = ReactServerDOMClient.encodeReply(
+      {promise: infinitePromise},
+      {
+        signal: controller.signal,
+      },
+    );
+    controller.abort();
+    const body = await promiseForResult;
+
+    const decoded = await ReactServerDOMServer.decodeReply(
+      body,
+      webpackServerMap,
+    );
+
+    let error = null;
+    try {
+      await decoded.promise;
+    } catch (x) {
+      error = x;
+    }
+    expect(error).not.toBe(null);
+    expect(error.message).toBe('Connection closed.');
+  });
 });
diff --git a/packages/react-server/src/ReactFlightReplyServer.js b/packages/react-server/src/ReactFlightReplyServer.js
index 930998ea3d889..4db7571bb66a6 100644
--- a/packages/react-server/src/ReactFlightReplyServer.js
+++ b/packages/react-server/src/ReactFlightReplyServer.js
@@ -169,6 +169,8 @@ export type Response = {
   _prefix: string,
   _formData: FormData,
   _chunks: Map<number, SomeChunk<any>>,
+  _closed: boolean,
+  _closedReason: mixed,
   _temporaryReferences: void | TemporaryReferenceSet,
 };
 
@@ -255,6 +257,14 @@ function createResolvedModelChunk<T>(
   return new Chunk(RESOLVED_MODEL, value, id, response);
 }
 
+function createErroredChunk<T>(
+  response: Response,
+  reason: mixed,
+): ErroredChunk<T> {
+  // $FlowFixMe[invalid-constructor] Flow doesn't support functions as constructors
+  return new Chunk(ERRORED, null, reason, response);
+}
+
 function resolveModelChunk<T>(
   chunk: SomeChunk<T>,
   value: string,
@@ -493,6 +503,8 @@ function initializeModelChunk<T>(chunk: ResolvedModelChunk<T>): void {
 // Report that any missing chunks in the model is now going to throw this
 // error upon read. Also notify any pending promises.
 export function reportGlobalError(response: Response, error: Error): void {
+  response._closed = true;
+  response._closedReason = error;
   response._chunks.forEach(chunk => {
     // If this chunk was already resolved or errored, it won't
     // trigger an error but if it wasn't then we need to
@@ -514,6 +526,10 @@ function getChunk(response: Response, id: number): SomeChunk<any> {
     if (backingEntry != null) {
       // We assume that this is a string entry for now.
       chunk = createResolvedModelChunk(response, (backingEntry: any), id);
+    } else if (response._closed) {
+      // We have already errored the response and we're not going to get
+      // anything more streaming in so this will immediately error.
+      chunk = createErroredChunk(response, response._closedReason);
     } else {
       // We're still waiting on this entry to stream in.
       chunk = createPendingChunk(response);
@@ -1082,6 +1098,8 @@ export function createResponse(
     _prefix: formFieldPrefix,
     _formData: backingFormData,
     _chunks: chunks,
+    _closed: false,
+    _closedReason: null,
     _temporaryReferences: temporaryReferences,
   };
   return response;
diff --git a/packages/react/src/__tests__/ReactStrictMode-test.js b/packages/react/src/__tests__/ReactStrictMode-test.js
index 863f84ebdb291..f28c70a871665 100644
--- a/packages/react/src/__tests__/ReactStrictMode-test.js
+++ b/packages/react/src/__tests__/ReactStrictMode-test.js
@@ -202,7 +202,7 @@ describe('ReactStrictMode', () => {
     expect(instance.state.count).toBe(2);
   });
 
-  // @gate debugRenderPhaseSideEffectsForStrictMode
+  // @gate __DEV__
   it('double invokes useState and useReducer initializers functions', async () => {
     const log = [];
 
@@ -390,7 +390,7 @@ describe('ReactStrictMode', () => {
     expect(instance.state.count).toBe(2);
   });
 
-  // @gate debugRenderPhaseSideEffectsForStrictMode
+  // @gate __DEV__
   it('double invokes useMemo functions', async () => {
     let log = [];
 
@@ -436,7 +436,7 @@ describe('ReactStrictMode', () => {
     ]);
   });
 
-  // @gate debugRenderPhaseSideEffectsForStrictMode
+  // @gate __DEV__
   it('double invokes useMemo functions with first result', async () => {
     let log = [];
     function Uppercased({text}) {
@@ -499,7 +499,7 @@ describe('ReactStrictMode', () => {
     expect(log[2]).toBe(log[3]);
   });
 
-  // @gate debugRenderPhaseSideEffectsForStrictMode
+  // @gate __DEV__
   it('double invokes setState updater functions', async () => {
     const log = [];
 
@@ -532,7 +532,7 @@ describe('ReactStrictMode', () => {
     expect(log).toEqual(['Compute count: 1', 'Compute count: 1']);
   });
 
-  // @gate debugRenderPhaseSideEffectsForStrictMode
+  // @gate __DEV__
   it('double invokes reducer functions', async () => {
     const log = [];
 
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index 8540d6e14721a..3046f8f4cb45e 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -186,12 +186,6 @@ export const disableLegacyContext = true;
  */
 export const disableLegacyContextForFunctionComponents = true;
 
-// Not ready to break experimental yet.
-// Modern <StrictMode /> behaviour aligns more with what components
-// components will encounter in production, especially when used With <Offscreen />.
-// TODO: clean up legacy <StrictMode /> once tests pass WWW.
-export const useModernStrictMode = true;
-
 // Enable the moveBefore() alternative to insertBefore(). This preserves states of moves.
 export const enableMoveBefore = false;
 
@@ -240,10 +234,6 @@ export const disableTextareaChildren = false;
 // Debugging and DevTools
 // -----------------------------------------------------------------------------
 
-// Helps identify side effects in render-phase lifecycle hooks and setState
-// reducers by double invoking them in StrictLegacyMode.
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
-
 // Gather advanced timing metrics for Profiler subtrees.
 export const enableProfilerTimer = __PROFILE__;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index 45807e9d876af..4ea9499e6ca80 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -32,7 +32,6 @@ export const {
 } = dynamicFlags;
 
 // The rest of the flags are static for better dead code elimination.
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
 export const disableClientCache = true;
 export const disableCommentsAsDOMContainers = true;
 export const disableDefaultPropsExceptForClasses = true;
@@ -80,7 +79,6 @@ export const renameElementSymbol = false;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableHydrationLaneScheduling = true;
 export const enableYieldingBeforePassive = false;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index c29da18a42055..dddd80aeea82a 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -12,12 +12,8 @@ import typeof * as ExportsType from './ReactFeatureFlags.native-oss';
 
 // TODO: Align these flags with canary and delete this file once RN ships from Canary.
 
-// DEV-only but enabled in the next RN Major.
-// Not supported by flag script to avoid the special case.
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
-
 // -----------------------------------------------------------------------------
-// All other flags
+// All flags
 // -----------------------------------------------------------------------------
 export const alwaysThrottleRetries = false;
 export const disableClientCache = true;
@@ -70,7 +66,6 @@ export const renameElementSymbol = true;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = false;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index df58c53eda9a4..95826007dc9cd 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -10,7 +10,6 @@
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.test-renderer';
 
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
 export const enableAsyncDebugInfo = false;
 export const enableSchedulingProfiler = false;
 export const enableProfilerTimer = __PROFILE__;
@@ -52,7 +51,6 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = true;
 export const enableDeferRootSchedulingToMicrotask = true;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
index a4dc5cb76d109..8d38112b16879 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
@@ -11,7 +11,6 @@ import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.test-renderer';
 
 export const alwaysThrottleRetries = false;
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
 export const disableClientCache = true;
 export const disableCommentsAsDOMContainers = true;
 export const disableDefaultPropsExceptForClasses = true;
@@ -65,7 +64,6 @@ export const renameElementSymbol = false;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableFabricCompleteRootInCommitPhase = false;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = true;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index e7c92602a0abf..28a303a034cac 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -10,7 +10,6 @@
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.test-renderer.www';
 
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
 export const enableAsyncDebugInfo = false;
 export const enableSchedulingProfiler = false;
 export const enableProfilerTimer = __PROFILE__;
@@ -54,7 +53,6 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = false;
 export const enableDeferRootSchedulingToMicrotask = true;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index da62754a13359..cf514f93d43ac 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -42,7 +42,6 @@ export const {
 // On WWW, __EXPERIMENTAL__ is used for a new modern build.
 // It's not used anywhere in production yet.
 
-export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
 export const enableProfilerTimer = __PROFILE__;
 export const enableProfilerCommitHooks = __PROFILE__;
 export const enableProfilerNestedUpdatePhase = __PROFILE__;
@@ -106,7 +105,6 @@ export const disableClientCache = true;
 export const enableServerComponentLogs = true;
 
 export const enableReactTestRendererWarning = false;
-export const useModernStrictMode = true;
 
 export const disableLegacyMode = true;