diff --git a/packages/react-dom/src/client/ReactDOM.js b/packages/react-dom/src/client/ReactDOM.js
index ee54497f232..2ca128485b6 100644
--- a/packages/react-dom/src/client/ReactDOM.js
+++ b/packages/react-dom/src/client/ReactDOM.js
@@ -37,6 +37,7 @@ import {
   attemptHydrationAtCurrentPriority,
   act,
 } from 'react-reconciler/inline.dom';
+import {getIsHydrating} from 'react-reconciler/src/ReactFiberHydrationContext';
 import {createPortal as createPortalImpl} from 'shared/ReactPortal';
 import {canUseDOM} from 'shared/ExecutionEnvironment';
 import {setBatchingImplementation} from 'legacy-events/ReactGenericBatching';
@@ -56,6 +57,7 @@ import ReactVersion from 'shared/ReactVersion';
 import invariant from 'shared/invariant';
 import {
   exposeConcurrentModeAPIs,
+  disableLegacyReactDOMAPIs,
   disableUnstableCreatePortal,
   disableUnstableRenderSubtreeIntoContainer,
   warnUnstableRenderSubtreeIntoContainer,
@@ -133,12 +135,6 @@ function createPortal(
 const ReactDOM: Object = {
   createPortal,
 
-  // Legacy
-  findDOMNode,
-  hydrate,
-  render,
-  unmountComponentAtNode,
-
   unstable_batchedUpdates: batchedUpdates,
 
   flushSync: flushSync,
@@ -166,6 +162,13 @@ const ReactDOM: Object = {
   version: ReactVersion,
 };
 
+if (!disableLegacyReactDOMAPIs) {
+  ReactDOM.findDOMNode = findDOMNode;
+  ReactDOM.hydrate = hydrate;
+  ReactDOM.render = render;
+  ReactDOM.unmountComponentAtNode = unmountComponentAtNode;
+}
+
 if (exposeConcurrentModeAPIs) {
   ReactDOM.createRoot = createRoot;
   ReactDOM.createBlockingRoot = createBlockingRoot;
@@ -179,6 +182,8 @@ if (exposeConcurrentModeAPIs) {
       queueExplicitHydrationTarget(target);
     }
   };
+
+  ReactDOM.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.getIsHydrating = getIsHydrating;
 }
 
 if (!disableUnstableRenderSubtreeIntoContainer) {
diff --git a/packages/react-dom/src/client/ReactDOMFB.js b/packages/react-dom/src/client/ReactDOMFB.js
index a995f485578..877c7d2ea3f 100644
--- a/packages/react-dom/src/client/ReactDOMFB.js
+++ b/packages/react-dom/src/client/ReactDOMFB.js
@@ -7,7 +7,6 @@
  * @flow
  */
 
-import {getIsHydrating} from 'react-reconciler/src/ReactFiberHydrationContext';
 import {addUserTimingListener} from 'shared/ReactFeatureFlags';
 
 import ReactDOM from './ReactDOM';
@@ -26,8 +25,6 @@ Object.assign(
     },
     // Perf experiment
     addUserTimingListener,
-
-    getIsHydrating,
   },
 );
 
diff --git a/packages/react-dom/src/events/forks/EventListener-www.js b/packages/react-dom/src/events/forks/EventListener.www-classic.js
similarity index 93%
rename from packages/react-dom/src/events/forks/EventListener-www.js
rename to packages/react-dom/src/events/forks/EventListener.www-classic.js
index 99b337f0e78..c433976289f 100644
--- a/packages/react-dom/src/events/forks/EventListener-www.js
+++ b/packages/react-dom/src/events/forks/EventListener.www-classic.js
@@ -10,7 +10,7 @@
 const EventListenerWWW = require('EventListener');
 
 import typeof * as EventListenerType from '../EventListener';
-import typeof * as EventListenerShimType from './EventListener-www';
+import typeof * as EventListenerShimType from './EventListener.www-classic';
 
 export function addEventBubbleListener(
   element: Element,
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index 792cd1def4d..a5111621992 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -425,7 +425,9 @@ export function createWorkInProgress(
 
     if (__DEV__) {
       // DEV-only fields
-      workInProgress._debugID = current._debugID;
+      if (enableUserTimingAPI) {
+        workInProgress._debugID = current._debugID;
+      }
       workInProgress._debugSource = current._debugSource;
       workInProgress._debugOwner = current._debugOwner;
       workInProgress._debugHookTypes = current._debugHookTypes;
@@ -958,7 +960,9 @@ export function assignFiberPropertiesInDEV(
     target.selfBaseDuration = source.selfBaseDuration;
     target.treeBaseDuration = source.treeBaseDuration;
   }
-  target._debugID = source._debugID;
+  if (enableUserTimingAPI) {
+    target._debugID = source._debugID;
+  }
   target._debugSource = source._debugSource;
   target._debugOwner = source._debugOwner;
   target._debugIsCurrentlyTiming = source._debugIsCurrentlyTiming;
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index c73997f1dce..ad9c544c06a 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -114,6 +114,8 @@ export const disableLegacyContext = false;
 // Disables React.createFactory
 export const disableCreateFactory = false;
 
+export const disableLegacyReactDOMAPIs = false;
+
 // Disables children for <textarea> elements
 export const disableTextareaChildren = false;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index c930e0ecc9b..3d37d7c0687 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -46,6 +46,7 @@ export const disableSchedulerTimeoutBasedOnReactExpirationTime = false;
 export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index ee795fe1e03..9d1649f97eb 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -41,6 +41,7 @@ export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const enableNativeTargetAsInstance = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.persistent.js b/packages/shared/forks/ReactFeatureFlags.persistent.js
index db307747c1b..907795d6a5b 100644
--- a/packages/shared/forks/ReactFeatureFlags.persistent.js
+++ b/packages/shared/forks/ReactFeatureFlags.persistent.js
@@ -41,6 +41,7 @@ export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const enableNativeTargetAsInstance = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index 5d8263c7208..fd17ee246ef 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -41,6 +41,7 @@ export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const enableNativeTargetAsInstance = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index ee17330bb47..fbeac2f0415 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -39,6 +39,7 @@ export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const enableNativeTargetAsInstance = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.testing.js b/packages/shared/forks/ReactFeatureFlags.testing.js
index 13fcc7e1980..b1817f02f10 100644
--- a/packages/shared/forks/ReactFeatureFlags.testing.js
+++ b/packages/shared/forks/ReactFeatureFlags.testing.js
@@ -41,6 +41,7 @@ export const enableTrainModelFix = true;
 export const enableTrustedTypesIntegration = false;
 export const enableNativeTargetAsInstance = false;
 export const disableCreateFactory = false;
+export const disableLegacyReactDOMAPIs = false;
 export const disableTextareaChildren = false;
 export const disableMapsAsChildren = false;
 export const disableUnstableRenderSubtreeIntoContainer = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www-classic.js
similarity index 98%
rename from packages/shared/forks/ReactFeatureFlags.www.js
rename to packages/shared/forks/ReactFeatureFlags.www-classic.js
index 74f346b017b..f42c637778a 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www-classic.js
@@ -8,7 +8,7 @@
  */
 
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
-import typeof * as FeatureFlagsShimType from './ReactFeatureFlags.www';
+import typeof * as FeatureFlagsShimType from './ReactFeatureFlags.www-classic';
 
 // Re-export dynamic flags from the www version.
 export const {
@@ -94,6 +94,8 @@ export const enableNativeTargetAsInstance = false;
 
 export const disableCreateFactory = false;
 
+export const disableLegacyReactDOMAPIs = false;
+
 export const disableTextareaChildren = false;
 
 export const disableMapsAsChildren = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.www-modern.js b/packages/shared/forks/ReactFeatureFlags.www-modern.js
new file mode 100644
index 00000000000..2b1c8a45b38
--- /dev/null
+++ b/packages/shared/forks/ReactFeatureFlags.www-modern.js
@@ -0,0 +1,86 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
+import typeof * as FeatureFlagsShimType from './ReactFeatureFlags.www-modern';
+
+// Re-export dynamic flags from the www version.
+export const {
+  debugRenderPhaseSideEffectsForStrictMode,
+  disableInputAttributeSyncing,
+  enableTrustedTypesIntegration,
+  deferPassiveEffectCleanupDuringUnmount,
+  warnAboutShorthandPropertyCollision,
+} = require('ReactFeatureFlags');
+
+export let enableUserTimingAPI = false;
+
+export const enableProfilerTimer = __PROFILE__;
+export const enableSchedulerTracing = __PROFILE__;
+export const enableSchedulerDebugging = true;
+
+export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
+export const warnAboutDeprecatedLifecycles = true;
+export const disableLegacyContext = true;
+export const warnAboutStringRefs = false;
+export const warnAboutDefaultPropsOnFunctionComponents = false;
+export const disableSchedulerTimeoutBasedOnReactExpirationTime = false;
+
+export const enableTrainModelFix = true;
+
+export const exposeConcurrentModeAPIs = __EXPERIMENTAL__;
+
+export const enableSuspenseServerRenderer = true;
+export const enableSelectiveHydration = true;
+
+export const enableChunksAPI = __EXPERIMENTAL__;
+
+export const disableJavaScriptURLs = true;
+
+export function addUserTimingListener() {
+  throw new Error('Not implemented.');
+}
+
+export const enableDeprecatedFlareAPI = true;
+
+export const enableFundamentalAPI = false;
+
+export const enableScopeAPI = true;
+
+export const enableJSXTransformAPI = true;
+
+export const warnAboutUnmockedScheduler = true;
+
+export const enableSuspenseCallback = true;
+
+export const flushSuspenseFallbacksInTests = true;
+
+export const enableNativeTargetAsInstance = false;
+
+export const disableCreateFactory = false;
+
+export const disableLegacyReactDOMAPIs = true;
+
+export const disableTextareaChildren = true;
+
+export const disableMapsAsChildren = true;
+
+export const disableUnstableRenderSubtreeIntoContainer = true;
+
+export const warnUnstableRenderSubtreeIntoContainer = false;
+
+export const disableUnstableCreatePortal = true;
+
+export const isTestEnvironment = false;
+
+// Flow magic to verify the exports of this file match the original version.
+// eslint-disable-next-line no-unused-vars
+type Check<_X, Y: _X, X: Y = _X> = null;
+// eslint-disable-next-line no-unused-expressions
+(null: Check<FeatureFlagsShimType, FeatureFlagsType>);
diff --git a/scripts/rollup/build.js b/scripts/rollup/build.js
index ec0cc2c1754..3e201df29ca 100644
--- a/scripts/rollup/build.js
+++ b/scripts/rollup/build.js
@@ -54,6 +54,9 @@ const {
   FB_WWW_DEV,
   FB_WWW_PROD,
   FB_WWW_PROFILING,
+  FB_WWW_MODERN_DEV,
+  FB_WWW_MODERN_PROD,
+  FB_WWW_MODERN_PROFILING,
   RN_OSS_DEV,
   RN_OSS_PROD,
   RN_OSS_PROFILING,
@@ -139,6 +142,9 @@ function getBabelConfig(
     case FB_WWW_DEV:
     case FB_WWW_PROD:
     case FB_WWW_PROFILING:
+    case FB_WWW_MODERN_DEV:
+    case FB_WWW_MODERN_PROD:
+    case FB_WWW_MODERN_PROFILING:
       return Object.assign({}, options, {
         plugins: options.plugins.concat([
           // Minify invariant messages
@@ -214,6 +220,9 @@ function getFormat(bundleType) {
     case FB_WWW_DEV:
     case FB_WWW_PROD:
     case FB_WWW_PROFILING:
+    case FB_WWW_MODERN_DEV:
+    case FB_WWW_MODERN_PROD:
+    case FB_WWW_MODERN_PROFILING:
     case RN_OSS_DEV:
     case RN_OSS_PROD:
     case RN_OSS_PROFILING:
@@ -244,14 +253,20 @@ function getFilename(name, globalName, bundleType) {
     case RN_OSS_DEV:
     case RN_FB_DEV:
       return `${globalName}-dev.js`;
+    case FB_WWW_MODERN_DEV:
+      return `${globalName}Modern-dev.js`;
     case FB_WWW_PROD:
     case RN_OSS_PROD:
     case RN_FB_PROD:
       return `${globalName}-prod.js`;
+    case FB_WWW_MODERN_PROD:
+      return `${globalName}Modern-prod.js`;
     case FB_WWW_PROFILING:
     case RN_FB_PROFILING:
     case RN_OSS_PROFILING:
       return `${globalName}-profiling.js`;
+    case FB_WWW_MODERN_PROFILING:
+      return `${globalName}Modern-profiling.js`;
   }
 }
 
@@ -260,6 +275,7 @@ function isProductionBundleType(bundleType) {
     case UMD_DEV:
     case NODE_DEV:
     case FB_WWW_DEV:
+    case FB_WWW_MODERN_DEV:
     case RN_OSS_DEV:
     case RN_FB_DEV:
       return false;
@@ -269,6 +285,8 @@ function isProductionBundleType(bundleType) {
     case NODE_PROFILING:
     case FB_WWW_PROD:
     case FB_WWW_PROFILING:
+    case FB_WWW_MODERN_PROD:
+    case FB_WWW_MODERN_PROFILING:
     case RN_OSS_PROD:
     case RN_OSS_PROFILING:
     case RN_FB_PROD:
@@ -283,6 +301,8 @@ function isProfilingBundleType(bundleType) {
   switch (bundleType) {
     case FB_WWW_DEV:
     case FB_WWW_PROD:
+    case FB_WWW_MODERN_DEV:
+    case FB_WWW_MODERN_PROD:
     case NODE_DEV:
     case NODE_PROD:
     case RN_FB_DEV:
@@ -293,6 +313,7 @@ function isProfilingBundleType(bundleType) {
     case UMD_PROD:
       return false;
     case FB_WWW_PROFILING:
+    case FB_WWW_MODERN_PROFILING:
     case NODE_PROFILING:
     case RN_FB_PROFILING:
     case RN_OSS_PROFILING:
@@ -336,10 +357,15 @@ function getPlugins(
     bundleType === UMD_DEV ||
     bundleType === UMD_PROD ||
     bundleType === UMD_PROFILING;
-  const isFBBundle =
+  const isFBClassicBundle =
     bundleType === FB_WWW_DEV ||
     bundleType === FB_WWW_PROD ||
     bundleType === FB_WWW_PROFILING;
+  const isFBModernBundle =
+    bundleType === FB_WWW_MODERN_DEV ||
+    bundleType === FB_WWW_MODERN_PROD ||
+    bundleType === FB_WWW_MODERN_PROFILING;
+  const isFBBundle = isFBClassicBundle || isFBModernBundle;
   const isRNBundle =
     bundleType === RN_OSS_DEV ||
     bundleType === RN_OSS_PROD ||
@@ -485,11 +511,19 @@ async function createBundle(bundle, bundleType) {
   const packageName = Packaging.getPackageName(bundle.entry);
 
   let resolvedEntry = require.resolve(bundle.entry);
-  const isFBBundle =
+  const isFBClassicBundle =
     bundleType === FB_WWW_DEV ||
     bundleType === FB_WWW_PROD ||
     bundleType === FB_WWW_PROFILING;
-  if (isFBBundle) {
+  const isFBModernBundle =
+    bundleType === FB_WWW_MODERN_DEV ||
+    bundleType === FB_WWW_MODERN_PROD ||
+    bundleType === FB_WWW_MODERN_PROFILING;
+  const isFBBundle = isFBClassicBundle || isFBModernBundle;
+
+  if (isFBClassicBundle) {
+    // Only do this for the classis bundles so that modern entry points
+    // match the ones we use in the open source.
     const resolvedFBEntry = resolvedEntry.replace('.js', '.fb.js');
     if (fs.existsSync(resolvedFBEntry)) {
       resolvedEntry = resolvedFBEntry;
@@ -545,7 +579,10 @@ async function createBundle(bundle, bundleType) {
     legacy:
       bundleType === FB_WWW_DEV ||
       bundleType === FB_WWW_PROD ||
-      bundleType === FB_WWW_PROFILING,
+      bundleType === FB_WWW_PROFILING ||
+      bundleType === FB_WWW_MODERN_DEV ||
+      bundleType === FB_WWW_MODERN_PROD ||
+      bundleType === FB_WWW_MODERN_PROFILING,
   };
   const [mainOutputPath, ...otherOutputPaths] = Packaging.getBundleOutputPaths(
     bundleType,
@@ -695,6 +732,9 @@ async function buildEverything() {
         [bundle, FB_WWW_DEV],
         [bundle, FB_WWW_PROD],
         [bundle, FB_WWW_PROFILING],
+        [bundle, FB_WWW_MODERN_DEV],
+        [bundle, FB_WWW_MODERN_PROD],
+        [bundle, FB_WWW_MODERN_PROFILING],
         [bundle, RN_FB_DEV],
         [bundle, RN_FB_PROD],
         [bundle, RN_FB_PROFILING]
diff --git a/scripts/rollup/bundles.js b/scripts/rollup/bundles.js
index fd262e49f40..557de96ce4e 100644
--- a/scripts/rollup/bundles.js
+++ b/scripts/rollup/bundles.js
@@ -10,6 +10,9 @@ const bundleTypes = {
   FB_WWW_DEV: 'FB_WWW_DEV',
   FB_WWW_PROD: 'FB_WWW_PROD',
   FB_WWW_PROFILING: 'FB_WWW_PROFILING',
+  FB_WWW_MODERN_DEV: 'FB_WWW_MODERN_DEV',
+  FB_WWW_MODERN_PROD: 'FB_WWW_MODERN_PROD',
+  FB_WWW_MODERN_PROFILING: 'FB_WWW_MODERN_PROFILING',
   RN_OSS_DEV: 'RN_OSS_DEV',
   RN_OSS_PROD: 'RN_OSS_PROD',
   RN_OSS_PROFILING: 'RN_OSS_PROFILING',
@@ -28,6 +31,9 @@ const {
   FB_WWW_DEV,
   FB_WWW_PROD,
   FB_WWW_PROFILING,
+  FB_WWW_MODERN_DEV,
+  FB_WWW_MODERN_PROD,
+  FB_WWW_MODERN_PROFILING,
   RN_OSS_DEV,
   RN_OSS_PROD,
   RN_OSS_PROFILING,
@@ -88,6 +94,9 @@ const bundles = [
       FB_WWW_DEV,
       FB_WWW_PROD,
       FB_WWW_PROFILING,
+      FB_WWW_MODERN_DEV,
+      FB_WWW_MODERN_PROD,
+      FB_WWW_MODERN_PROFILING,
     ],
     moduleType: RENDERER,
     entry: 'react-dom',
diff --git a/scripts/rollup/forks.js b/scripts/rollup/forks.js
index 9f1f3c41bdd..26b79aefc33 100644
--- a/scripts/rollup/forks.js
+++ b/scripts/rollup/forks.js
@@ -10,6 +10,9 @@ const {
   FB_WWW_DEV,
   FB_WWW_PROD,
   FB_WWW_PROFILING,
+  FB_WWW_MODERN_DEV,
+  FB_WWW_MODERN_PROD,
+  FB_WWW_MODERN_PROFILING,
   RN_OSS_DEV,
   RN_OSS_PROD,
   RN_OSS_PROFILING,
@@ -103,6 +106,9 @@ const forks = Object.freeze({
           case FB_WWW_DEV:
           case FB_WWW_PROD:
           case FB_WWW_PROFILING:
+          case FB_WWW_MODERN_DEV:
+          case FB_WWW_MODERN_PROD:
+          case FB_WWW_MODERN_PROFILING:
             return 'shared/forks/ReactFeatureFlags.test-renderer.www.js';
         }
         return 'shared/forks/ReactFeatureFlags.test-renderer.js';
@@ -115,7 +121,11 @@ const forks = Object.freeze({
           case FB_WWW_DEV:
           case FB_WWW_PROD:
           case FB_WWW_PROFILING:
-            return 'shared/forks/ReactFeatureFlags.www.js';
+            return 'shared/forks/ReactFeatureFlags.www-classic.js';
+          case FB_WWW_MODERN_DEV:
+          case FB_WWW_MODERN_PROD:
+          case FB_WWW_MODERN_PROFILING:
+            return 'shared/forks/ReactFeatureFlags.www-modern.js';
         }
     }
     return null;
@@ -163,7 +173,10 @@ const forks = Object.freeze({
     if (
       bundleType === FB_WWW_DEV ||
       bundleType === FB_WWW_PROD ||
-      bundleType === FB_WWW_PROFILING
+      bundleType === FB_WWW_PROFILING ||
+      bundleType === FB_WWW_MODERN_DEV ||
+      bundleType === FB_WWW_MODERN_PROD ||
+      bundleType === FB_WWW_MODERN_PROFILING
     ) {
       return 'scheduler/src/forks/SchedulerFeatureFlags.www.js';
     }
@@ -185,6 +198,7 @@ const forks = Object.freeze({
   'shared/consoleWithStackDev': (bundleType, entry) => {
     switch (bundleType) {
       case FB_WWW_DEV:
+      case FB_WWW_MODERN_DEV:
         return 'shared/forks/consoleWithStackDev.www.js';
       default:
         return null;
@@ -198,6 +212,9 @@ const forks = Object.freeze({
       case FB_WWW_DEV:
       case FB_WWW_PROD:
       case FB_WWW_PROFILING:
+      case FB_WWW_MODERN_DEV:
+      case FB_WWW_MODERN_PROD:
+      case FB_WWW_MODERN_PROFILING:
         return 'react/src/forks/ReactCurrentOwner.www.js';
       default:
         return null;
@@ -211,6 +228,9 @@ const forks = Object.freeze({
       case FB_WWW_DEV:
       case FB_WWW_PROD:
       case FB_WWW_PROFILING:
+      case FB_WWW_MODERN_DEV:
+      case FB_WWW_MODERN_PROD:
+      case FB_WWW_MODERN_PROFILING:
         return 'react/src/forks/ReactCurrentDispatcher.www.js';
       default:
         return null;
@@ -234,6 +254,9 @@ const forks = Object.freeze({
       case FB_WWW_DEV:
       case FB_WWW_PROD:
       case FB_WWW_PROFILING:
+      case FB_WWW_MODERN_DEV:
+      case FB_WWW_MODERN_PROD:
+      case FB_WWW_MODERN_PROFILING:
         return 'shared/forks/invokeGuardedCallbackImpl.www.js';
       default:
         return null;
@@ -246,6 +269,9 @@ const forks = Object.freeze({
       case FB_WWW_DEV:
       case FB_WWW_PROD:
       case FB_WWW_PROFILING:
+      case FB_WWW_MODERN_DEV:
+      case FB_WWW_MODERN_PROD:
+      case FB_WWW_MODERN_PROFILING:
         // Use the www fork which shows an error dialog.
         return 'react-reconciler/src/forks/ReactFiberErrorDialog.www.js';
       case RN_OSS_DEV:
@@ -376,14 +402,14 @@ const forks = Object.freeze({
     );
   },
 
-  // We wrap top-level listeners into guards on www.
+  // We wrap top-level listeners into guards on www classic builds.
   'react-dom/src/events/EventListener': (bundleType, entry) => {
     switch (bundleType) {
       case FB_WWW_DEV:
       case FB_WWW_PROD:
       case FB_WWW_PROFILING:
         // Use the www fork which is integrated with TimeSlice profiling.
-        return 'react-dom/src/events/forks/EventListener-www.js';
+        return 'react-dom/src/events/forks/EventListener.www-classic.js';
       default:
         return null;
     }
diff --git a/scripts/rollup/packaging.js b/scripts/rollup/packaging.js
index c5ed04df5ab..c265cd2559d 100644
--- a/scripts/rollup/packaging.js
+++ b/scripts/rollup/packaging.js
@@ -19,6 +19,9 @@ const {
   FB_WWW_DEV,
   FB_WWW_PROD,
   FB_WWW_PROFILING,
+  FB_WWW_MODERN_DEV,
+  FB_WWW_MODERN_PROD,
+  FB_WWW_MODERN_PROFILING,
   RN_OSS_DEV,
   RN_OSS_PROD,
   RN_OSS_PROFILING,
@@ -50,6 +53,9 @@ function getBundleOutputPaths(bundleType, filename, packageName) {
     case FB_WWW_DEV:
     case FB_WWW_PROD:
     case FB_WWW_PROFILING:
+    case FB_WWW_MODERN_DEV:
+    case FB_WWW_MODERN_PROD:
+    case FB_WWW_MODERN_PROFILING:
       return [`build/facebook-www/${filename}`];
     case RN_OSS_DEV:
     case RN_OSS_PROD:
diff --git a/scripts/rollup/wrappers.js b/scripts/rollup/wrappers.js
index f9ca412c436..a695e904b09 100644
--- a/scripts/rollup/wrappers.js
+++ b/scripts/rollup/wrappers.js
@@ -13,6 +13,9 @@ const {
   FB_WWW_DEV,
   FB_WWW_PROD,
   FB_WWW_PROFILING,
+  FB_WWW_MODERN_DEV,
+  FB_WWW_MODERN_PROD,
+  FB_WWW_MODERN_PROFILING,
   RN_OSS_DEV,
   RN_OSS_PROD,
   RN_OSS_PROFILING,
@@ -169,6 +172,51 @@ ${license}
  * @preserve-invariant-messages
  */
 
+${source}`;
+  },
+
+  /****************** FB_WWW_MODERN_DEV ******************/
+  [FB_WWW_MODERN_DEV](source, globalName, filename, moduleType) {
+    return `/**
+${license}
+ *
+ * @noflow
+ * @preventMunge
+ * @preserve-invariant-messages
+ */
+
+'use strict';
+
+if (__DEV__) {
+  (function() {
+${source}
+  })();
+}`;
+  },
+
+  /****************** FB_WWW_MODERN_PROD ******************/
+  [FB_WWW_MODERN_PROD](source, globalName, filename, moduleType) {
+    return `/**
+${license}
+ *
+ * @noflow
+ * @preventMunge
+ * @preserve-invariant-messages
+ */
+
+${source}`;
+  },
+
+  /****************** FB_WWW_MODERN_PROFILING ******************/
+  [FB_WWW_MODERN_PROFILING](source, globalName, filename, moduleType) {
+    return `/**
+${license}
+ *
+ * @noflow
+ * @preventMunge
+ * @preserve-invariant-messages
+ */
+
 ${source}`;
   },