diff --git a/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js b/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
index 7fef11051116..8a07dfefb0fe 100644
--- a/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
+++ b/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
@@ -38,6 +38,8 @@ import {getParentHydrationBoundary} from './ReactFiberConfigDOM';
 
 import {enableScopeAPI} from 'shared/ReactFeatureFlags';
 
+import {enableInternalInstanceMap} from 'shared/ReactFeatureFlags';
+
 const randomKey = Math.random().toString(36).slice(2);
 const internalInstanceKey = '__reactFiber$' + randomKey;
 const internalPropsKey = '__reactProps$' + randomKey;
@@ -49,7 +51,32 @@ const internalRootNodeResourcesKey = '__reactResources$' + randomKey;
 const internalHoistableMarker = '__reactMarker$' + randomKey;
 const internalScrollTimer = '__reactScroll$' + randomKey;
 
+type InstanceUnion =
+  | Instance
+  | TextInstance
+  | SuspenseInstance
+  | ActivityInstance
+  | ReactScopeInstance
+  | Container;
+
+const PossiblyWeakMap = typeof WeakMap === 'function' ? WeakMap : Map;
+const internalInstanceMap:
+  | WeakMap<InstanceUnion, Fiber>
+  | Map<InstanceUnion, Fiber> = new PossiblyWeakMap();
+const internalPropsMap:
+  | WeakMap<InstanceUnion, Props>
+  | Map<InstanceUnion, Props> = new PossiblyWeakMap();
+
 export function detachDeletedInstance(node: Instance): void {
+  if (enableInternalInstanceMap) {
+    internalInstanceMap.delete(node);
+    internalPropsMap.delete(node);
+    delete (node: any)[internalEventHandlersKey];
+    delete (node: any)[internalEventHandlerListenersKey];
+    delete (node: any)[internalEventHandlesSetKey];
+    delete (node: any)[internalRootNodeResourcesKey];
+    return;
+  }
   // TODO: This function is only called on host components. I don't think all of
   // these fields are relevant.
   delete (node: any)[internalInstanceKey];
@@ -68,6 +95,10 @@ export function precacheFiberNode(
     | ActivityInstance
     | ReactScopeInstance,
 ): void {
+  if (enableInternalInstanceMap) {
+    internalInstanceMap.set(node, hostInst);
+    return;
+  }
   (node: any)[internalInstanceKey] = hostInst;
 }
 
@@ -95,7 +126,12 @@ export function isContainerMarkedAsRoot(node: Container): boolean {
 // HostRoot back. To get to the HostRoot, you need to pass a child of it.
 // The same thing applies to Suspense and Activity boundaries.
 export function getClosestInstanceFromNode(targetNode: Node): null | Fiber {
-  let targetInst = (targetNode: any)[internalInstanceKey];
+  let targetInst: void | Fiber;
+  if (enableInternalInstanceMap) {
+    targetInst = internalInstanceMap.get(((targetNode: any): InstanceUnion));
+  } else {
+    targetInst = (targetNode: any)[internalInstanceKey];
+  }
   if (targetInst) {
     // Don't return HostRoot, SuspenseComponent or ActivityComponent here.
     return targetInst;
@@ -112,9 +148,15 @@ export function getClosestInstanceFromNode(targetNode: Node): null | Fiber {
     // itself because the fibers are conceptually between the container
     // node and the first child. It isn't surrounding the container node.
     // If it's not a container, we check if it's an instance.
-    targetInst =
-      (parentNode: any)[internalContainerInstanceKey] ||
-      (parentNode: any)[internalInstanceKey];
+    if (enableInternalInstanceMap) {
+      targetInst =
+        (parentNode: any)[internalContainerInstanceKey] ||
+        internalInstanceMap.get(((parentNode: any): InstanceUnion));
+    } else {
+      targetInst =
+        (parentNode: any)[internalContainerInstanceKey] ||
+        (parentNode: any)[internalInstanceKey];
+    }
     if (targetInst) {
       // Since this wasn't the direct target of the event, we might have
       // stepped past dehydrated DOM nodes to get here. However they could
@@ -147,8 +189,10 @@ export function getClosestInstanceFromNode(targetNode: Node): null | Fiber {
           // have had an internalInstanceKey on it.
           // Let's get the fiber associated with the SuspenseComponent
           // as the deepest instance.
-          // $FlowFixMe[prop-missing]
-          const targetFiber = hydrationInstance[internalInstanceKey];
+          const targetFiber = enableInternalInstanceMap
+            ? internalInstanceMap.get(hydrationInstance)
+            : // $FlowFixMe[prop-missing]
+              hydrationInstance[internalInstanceKey];
           if (targetFiber) {
             return targetFiber;
           }
@@ -175,9 +219,16 @@ export function getClosestInstanceFromNode(targetNode: Node): null | Fiber {
  * instance, or null if the node was not rendered by this React.
  */
 export function getInstanceFromNode(node: Node): Fiber | null {
-  const inst =
-    (node: any)[internalInstanceKey] ||
-    (node: any)[internalContainerInstanceKey];
+  let inst: void | null | Fiber;
+  if (enableInternalInstanceMap) {
+    inst =
+      internalInstanceMap.get(((node: any): InstanceUnion)) ||
+      (node: any)[internalContainerInstanceKey];
+  } else {
+    inst =
+      (node: any)[internalInstanceKey] ||
+      (node: any)[internalContainerInstanceKey];
+  }
   if (inst) {
     const tag = inst.tag;
     if (
@@ -226,16 +277,24 @@ export function getFiberCurrentPropsFromNode(
     | TextInstance
     | SuspenseInstance
     | ActivityInstance,
-): Props {
+): Props | null {
+  if (enableInternalInstanceMap) {
+    return internalPropsMap.get(node) || null;
+  }
   return (node: any)[internalPropsKey] || null;
 }
 
 export function updateFiberProps(node: Instance, props: Props): void {
+  if (enableInternalInstanceMap) {
+    internalPropsMap.set(node, props);
+    return;
+  }
   (node: any)[internalPropsKey] = props;
 }
 
 export function getEventListenerSet(node: EventTarget): Set<string> {
-  let elementListenerSet = (node: any)[internalEventHandlersKey];
+  let elementListenerSet: Set<string> | void;
+  elementListenerSet = (node: any)[internalEventHandlersKey];
   if (elementListenerSet === undefined) {
     elementListenerSet = (node: any)[internalEventHandlersKey] = new Set();
   }
@@ -246,6 +305,9 @@ export function getFiberFromScopeInstance(
   scope: ReactScopeInstance,
 ): null | Fiber {
   if (enableScopeAPI) {
+    if (enableInternalInstanceMap) {
+      return internalInstanceMap.get(((scope: any): InstanceUnion)) || null;
+    }
     return (scope: any)[internalInstanceKey] || null;
   }
   return null;
@@ -318,6 +380,12 @@ export function clearScrollEndTimer(node: EventTarget): void {
 }
 
 export function isOwnedInstance(node: Node): boolean {
+  if (enableInternalInstanceMap) {
+    return !!(
+      (node: any)[internalHoistableMarker] ||
+      internalInstanceMap.has((node: any))
+    );
+  }
   return !!(
     (node: any)[internalHoistableMarker] || (node: any)[internalInstanceKey]
   );
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index c31809276bdb..a5befa11a0d5 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -147,6 +147,8 @@ export const enableFragmentRefs: boolean = true;
 export const enableFragmentRefsScrollIntoView: boolean = true;
 export const enableFragmentRefsInstanceHandles: boolean = false;
 
+export const enableInternalInstanceMap: boolean = false;
+
 // -----------------------------------------------------------------------------
 // Ready for next major.
 //
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index e1b26cdb83b3..71c64b9db03d 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -84,6 +84,7 @@ export const enableComponentPerformanceTrack: boolean =
   __PROFILE__ && dynamicFlags.enableComponentPerformanceTrack;
 export const enablePerformanceIssueReporting: boolean =
   enableComponentPerformanceTrack;
+export const enableInternalInstanceMap: boolean = false;
 
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index 3880556d247f..cf765d7d6899 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -76,6 +76,8 @@ export const enableFragmentRefs: boolean = true;
 export const enableFragmentRefsScrollIntoView: boolean = false;
 export const enableFragmentRefsInstanceHandles: boolean = false;
 
+export const enableInternalInstanceMap: boolean = false;
+
 // Profiling Only
 export const enableProfilerTimer: boolean = __PROFILE__;
 export const enableProfilerCommitHooks: boolean = __PROFILE__;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index 88c46d26e2eb..0747f0e8be43 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -77,6 +77,8 @@ export const enableFragmentRefs: boolean = true;
 export const enableFragmentRefsScrollIntoView: boolean = true;
 export const enableFragmentRefsInstanceHandles: boolean = false;
 
+export const enableInternalInstanceMap: boolean = false;
+
 // TODO: This must be in sync with the main ReactFeatureFlags file because
 // the Test Renderer's value must be the same as the one used by the
 // react package.
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index d815fd7ddc8e..2b40c1b01c6c 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -85,5 +85,7 @@ export const enableFragmentRefsScrollIntoView: boolean = false;
 export const enableFragmentRefsInstanceHandles: boolean = false;
 export const ownerStackLimit = 1e4;
 
+export const enableInternalInstanceMap: boolean = false;
+
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);
diff --git a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
index 674aa5d32018..1d174609cb9c 100644
--- a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
+++ b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
@@ -38,6 +38,8 @@ export const enableFragmentRefs: boolean = __VARIANT__;
 export const enableFragmentRefsScrollIntoView: boolean = __VARIANT__;
 export const enableAsyncDebugInfo: boolean = __VARIANT__;
 
+export const enableInternalInstanceMap: boolean = __VARIANT__;
+
 // TODO: These flags are hard-coded to the default values used in open source.
 // Update the tests so that they pass in either mode, then set these
 // to __VARIANT__.
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index 4ace06ed4c49..029cd0d196e1 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -35,6 +35,7 @@ export const {
   enableFragmentRefs,
   enableFragmentRefsScrollIntoView,
   enableAsyncDebugInfo,
+  enableInternalInstanceMap,
 } = dynamicFeatureFlags;
 
 // On WWW, __EXPERIMENTAL__ is used for a new modern build.