diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index 2911b1bf5c549..c8b332b1542ea 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -38,6 +38,7 @@ import {
   enableDO_NOT_USE_disableStrictPassiveEffect,
   enableRenderableContext,
   disableLegacyMode,
+  enableObjectFiber,
   enableOwnerStacks,
 } from 'shared/ReactFeatureFlags';
 import {NoFlags, Placement, StaticMask} from './ReactFiberFlags';
@@ -232,7 +233,7 @@ function FiberNode(
 //    is faster.
 // 5) It should be easy to port this to a C struct and keep a C implementation
 //    compatible.
-function createFiber(
+function createFiberImplClass(
   tag: WorkTag,
   pendingProps: mixed,
   key: null | string,
@@ -242,6 +243,72 @@ function createFiber(
   return new FiberNode(tag, pendingProps, key, mode);
 }
 
+function createFiberImplObject(
+  tag: WorkTag,
+  pendingProps: mixed,
+  key: null | string,
+  mode: TypeOfMode,
+): Fiber {
+  const fiber: Fiber = {
+    // Instance
+    tag,
+    key,
+    elementType: null,
+    type: null,
+    stateNode: null,
+
+    // Fiber
+    return: null,
+    child: null,
+    sibling: null,
+    index: 0,
+
+    ref: null,
+    refCleanup: null,
+
+    pendingProps,
+    memoizedProps: null,
+    updateQueue: null,
+    memoizedState: null,
+    dependencies: null,
+
+    mode,
+
+    // Effects
+    flags: NoFlags,
+    subtreeFlags: NoFlags,
+    deletions: null,
+
+    lanes: NoLanes,
+    childLanes: NoLanes,
+
+    alternate: null,
+  };
+
+  if (enableProfilerTimer) {
+    fiber.actualDuration = 0;
+    fiber.actualStartTime = -1;
+    fiber.selfBaseDuration = 0;
+    fiber.treeBaseDuration = 0;
+  }
+
+  if (__DEV__) {
+    fiber._debugInfo = null;
+    fiber._debugOwner = null;
+    fiber._debugNeedsRemount = false;
+    fiber._debugHookTypes = null;
+
+    if (!hasBadMapPolyfill && typeof Object.preventExtensions === 'function') {
+      Object.preventExtensions(fiber);
+    }
+  }
+  return fiber;
+}
+
+const createFiber = enableObjectFiber
+  ? createFiberImplObject
+  : createFiberImplClass;
+
 function shouldConstruct(Component: Function) {
   const prototype = Component.prototype;
   return !!(prototype && prototype.isReactComponent);
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index b161ac7cb1141..a3280444766c7 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -87,6 +87,11 @@ export const enableTaint = __EXPERIMENTAL__;
 
 export const enablePostpone = __EXPERIMENTAL__;
 
+/**
+ * Switches Fiber creation to a simple object instead of a constructor.
+ */
+export const enableObjectFiber = false;
+
 export const enableTransitionTracing = false;
 
 // No known bugs, but needs performance testing
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js b/packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js
index a0513f81e7bf7..ae7d9bd844a21 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js
@@ -22,5 +22,6 @@ export const consoleManagedByDevToolsDuringStrictMode = __VARIANT__;
 export const disableDefaultPropsExceptForClasses = __VARIANT__;
 export const enableAddPropertiesFastPath = __VARIANT__;
 export const enableFastJSX = __VARIANT__;
+export const enableObjectFiber = __VARIANT__;
 export const enableShallowPropDiffing = __VARIANT__;
 export const passChildrenWhenCloningPersistedNodes = __VARIANT__;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index 353937a7eaed8..0939b459a9b40 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -24,6 +24,7 @@ export const {
   disableDefaultPropsExceptForClasses,
   enableAddPropertiesFastPath,
   enableFastJSX,
+  enableObjectFiber,
   enableShallowPropDiffing,
   passChildrenWhenCloningPersistedNodes,
 } = dynamicFlags;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index e47a79ef7abb8..031f20247eda2 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -55,6 +55,7 @@ export const enableLegacyCache = false;
 export const enableLegacyFBSupport = false;
 export const enableLegacyHidden = false;
 export const enableNoCloningMemoCache = false;
+export const enableObjectFiber = false;
 export const enableOwnerStacks = __EXPERIMENTAL__;
 export const enablePostpone = false;
 export const enableReactTestRendererWarning = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index 717e16b88060c..172335d7cc735 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -96,6 +96,7 @@ export const enableRenderableContext = true;
 export const enableReactTestRendererWarning = true;
 export const disableDefaultPropsExceptForClasses = true;
 
+export const enableObjectFiber = false;
 export const enableOwnerStacks = false;
 
 // Flow magic to verify the exports of this file match the original version.
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
index 5d256ca9e06c1..cea3b6ada831d 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js
@@ -47,6 +47,7 @@ export const enableLegacyCache = false;
 export const enableLegacyFBSupport = false;
 export const enableLegacyHidden = false;
 export const enableNoCloningMemoCache = false;
+export const enableObjectFiber = false;
 export const enableOwnerStacks = false;
 export const enablePostpone = false;
 export const enableProfilerCommitHooks = __PROFILE__;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index 71f533f8d6d2a..bdc43fd844294 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -90,6 +90,7 @@ export const enableAddPropertiesFastPath = false;
 
 export const renameElementSymbol = false;
 
+export const enableObjectFiber = false;
 export const enableOwnerStacks = false;
 export const enableShallowPropDiffing = false;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index 66a3723071986..8c4773c3ed44a 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -120,6 +120,7 @@ export const disableStringRefs = false;
 export const disableLegacyMode: boolean =
   __EXPERIMENTAL__ || dynamicFeatureFlags.disableLegacyMode;
 
+export const enableObjectFiber = false;
 export const enableOwnerStacks = false;
 export const enableShallowPropDiffing = false;