diff --git a/package.json b/package.json
index 9dc97a27eb429..ec226416e2117 100644
--- a/package.json
+++ b/package.json
@@ -77,7 +77,6 @@
     "minimist": "^1.2.3",
     "mkdirp": "^0.5.1",
     "ncp": "^2.0.0",
-    "object-assign": "^4.1.1",
     "pacote": "^10.3.0",
     "prettier": "1.19.1",
     "prop-types": "^15.6.2",
diff --git a/packages/jest-react/package.json b/packages/jest-react/package.json
index 0a1c764be2fe7..78907eeb32c77 100644
--- a/packages/jest-react/package.json
+++ b/packages/jest-react/package.json
@@ -23,9 +23,6 @@
     "react": "^17.0.0",
     "react-test-renderer": "^17.0.0"
   },
-  "dependencies": {
-    "object-assign": "^4.1.1"
-  },
   "files": [
     "LICENSE",
     "README.md",
diff --git a/packages/react-art/npm/Circle.js b/packages/react-art/npm/Circle.js
index 1100a3e5a5b9f..4e0cca3a47eb9 100644
--- a/packages/react-art/npm/Circle.js
+++ b/packages/react-art/npm/Circle.js
@@ -17,7 +17,7 @@
 
 'use strict';
 
-var assign = require('object-assign');
+var assign = Object.assign;
 var PropTypes = require('prop-types');
 var React = require('react');
 var ReactART = require('react-art');
diff --git a/packages/react-art/npm/Rectangle.js b/packages/react-art/npm/Rectangle.js
index 54b33e69a1830..89f443e9ceecc 100644
--- a/packages/react-art/npm/Rectangle.js
+++ b/packages/react-art/npm/Rectangle.js
@@ -24,7 +24,7 @@
 
 'use strict';
 
-var assign = require('object-assign');
+var assign = Object.assign;
 var PropTypes = require('prop-types');
 var React = require('react');
 var ReactART = require('react-art');
diff --git a/packages/react-art/npm/Wedge.js b/packages/react-art/npm/Wedge.js
index 91c8bc4158b8e..90de17e071f61 100644
--- a/packages/react-art/npm/Wedge.js
+++ b/packages/react-art/npm/Wedge.js
@@ -20,7 +20,7 @@
 
 'use strict';
 
-var assign = require('object-assign');
+var assign = Object.assign;
 var PropTypes = require('prop-types');
 var React = require('react');
 var ReactART = require('react-art');
diff --git a/packages/react-art/package.json b/packages/react-art/package.json
index fabdcd560f9ce..a819d3eb269a2 100644
--- a/packages/react-art/package.json
+++ b/packages/react-art/package.json
@@ -25,7 +25,6 @@
     "art": "^0.10.1",
     "create-react-class": "^15.6.2",
     "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1",
     "scheduler": "^0.20.1"
   },
   "peerDependencies": {
diff --git a/packages/react-client/package.json b/packages/react-client/package.json
index 7752fcb73f8a5..64670a870d8a8 100644
--- a/packages/react-client/package.json
+++ b/packages/react-client/package.json
@@ -27,8 +27,7 @@
     "react": "^17.0.0"
   },
   "dependencies": {
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1"
+    "loose-envify": "^1.1.0"
   },
   "browserify": {
     "transform": [
diff --git a/packages/react-debug-tools/package.json b/packages/react-debug-tools/package.json
index 69327edaeb1f3..f3ee5806f722a 100644
--- a/packages/react-debug-tools/package.json
+++ b/packages/react-debug-tools/package.json
@@ -28,7 +28,6 @@
     "react": "^17.0.0"
   },
   "dependencies": {
-    "error-stack-parser": "^2.0.2",
-    "object-assign": "^4.1.1"
+    "error-stack-parser": "^2.0.2"
   }
 }
diff --git a/packages/react-debug-tools/src/ReactDebugHooks.js b/packages/react-debug-tools/src/ReactDebugHooks.js
index 895e75359867c..0ffec00bd3f8d 100644
--- a/packages/react-debug-tools/src/ReactDebugHooks.js
+++ b/packages/react-debug-tools/src/ReactDebugHooks.js
@@ -20,6 +20,7 @@ import type {
 } from 'react-reconciler/src/ReactInternalTypes';
 
 import ErrorStackParser from 'error-stack-parser';
+import assign from 'shared/assign';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {
   FunctionComponent,
@@ -720,7 +721,7 @@ function inspectHooksOfForwardRef<Props, Ref>(
 function resolveDefaultProps(Component, baseProps) {
   if (Component && Component.defaultProps) {
     // Resolve default props. Taken from ReactElement
-    const props = Object.assign({}, baseProps);
+    const props = assign({}, baseProps);
     const defaultProps = Component.defaultProps;
     for (const propName in defaultProps) {
       if (props[propName] === undefined) {
diff --git a/packages/react-devtools-shared/src/backend/views/Highlighter/Overlay.js b/packages/react-devtools-shared/src/backend/views/Highlighter/Overlay.js
index 7e6cc595654b8..ba763562a1629 100644
--- a/packages/react-devtools-shared/src/backend/views/Highlighter/Overlay.js
+++ b/packages/react-devtools-shared/src/backend/views/Highlighter/Overlay.js
@@ -7,9 +7,10 @@
  * @flow
  */
 
-import assign from 'object-assign';
 import {getElementDimensions, getNestedBoundingClientRect} from '../utils';
 
+const assign = Object.assign;
+
 import type {DevToolsHook} from 'react-devtools-shared/src/backend/types';
 import type {Rect} from '../utils';
 
diff --git a/packages/react-dom/package.json b/packages/react-dom/package.json
index 71d15b5670dc5..25207ffc9c39f 100644
--- a/packages/react-dom/package.json
+++ b/packages/react-dom/package.json
@@ -18,7 +18,6 @@
   "homepage": "https://reactjs.org/",
   "dependencies": {
     "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1",
     "scheduler": "^0.20.1"
   },
   "peerDependencies": {
diff --git a/packages/react-dom/src/client/ReactDOMInput.js b/packages/react-dom/src/client/ReactDOMInput.js
index 8f5098405b576..a4b8dede45a73 100644
--- a/packages/react-dom/src/client/ReactDOMInput.js
+++ b/packages/react-dom/src/client/ReactDOMInput.js
@@ -16,6 +16,7 @@ import {getToStringValue, toString} from './ToStringValue';
 import {checkControlledValueProps} from '../shared/ReactControlledValuePropTypes';
 import {updateValueIfChanged} from './inputValueTracking';
 import getActiveElement from './getActiveElement';
+import assign from 'shared/assign';
 import {disableInputAttributeSyncing} from 'shared/ReactFeatureFlags';
 import {checkAttributeStringCoercion} from 'shared/CheckStringCoercion';
 
@@ -62,7 +63,7 @@ export function getHostProps(element: Element, props: Object) {
   const node = ((element: any): InputWithWrapperState);
   const checked = props.checked;
 
-  const hostProps = Object.assign({}, props, {
+  const hostProps = assign({}, props, {
     defaultChecked: undefined,
     defaultValue: undefined,
     value: undefined,
diff --git a/packages/react-dom/src/client/ReactDOMSelect.js b/packages/react-dom/src/client/ReactDOMSelect.js
index df336d4b92254..ece9275e4b37e 100644
--- a/packages/react-dom/src/client/ReactDOMSelect.js
+++ b/packages/react-dom/src/client/ReactDOMSelect.js
@@ -12,6 +12,7 @@ import {getCurrentFiberOwnerNameInDevOrNull} from 'react-reconciler/src/ReactCur
 
 import {checkControlledValueProps} from '../shared/ReactControlledValuePropTypes';
 import {getToStringValue, toString} from './ToStringValue';
+import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 
 let didWarnValueDefaultValue;
@@ -134,7 +135,7 @@ function updateOptions(
  */
 
 export function getHostProps(element: Element, props: Object) {
-  return Object.assign({}, props, {
+  return assign({}, props, {
     value: undefined,
   });
 }
diff --git a/packages/react-dom/src/events/SyntheticEvent.js b/packages/react-dom/src/events/SyntheticEvent.js
index 649cab082e61a..3609e6794a50d 100644
--- a/packages/react-dom/src/events/SyntheticEvent.js
+++ b/packages/react-dom/src/events/SyntheticEvent.js
@@ -9,6 +9,7 @@
 
 /* eslint valid-typeof: 0 */
 
+import assign from 'shared/assign';
 import getEventCharCode from './getEventCharCode';
 
 type EventInterfaceType = {
@@ -78,7 +79,7 @@ function createSyntheticEvent(Interface: EventInterfaceType) {
     return this;
   }
 
-  Object.assign(SyntheticBaseEvent.prototype, {
+  assign(SyntheticBaseEvent.prototype, {
     preventDefault: function() {
       this.defaultPrevented = true;
       const event = this.nativeEvent;
diff --git a/packages/react-dom/src/server/ReactPartialRenderer.js b/packages/react-dom/src/server/ReactPartialRenderer.js
index 1902dc65690c8..41c2885680437 100644
--- a/packages/react-dom/src/server/ReactPartialRenderer.js
+++ b/packages/react-dom/src/server/ReactPartialRenderer.js
@@ -80,6 +80,7 @@ import warnValidStyle from '../shared/warnValidStyle';
 import {validateProperties as validateARIAProperties} from '../shared/ReactDOMInvalidARIAHook';
 import {validateProperties as validateInputProperties} from '../shared/ReactDOMNullInputValuePropHook';
 import {validateProperties as validateUnknownProperties} from '../shared/ReactDOMUnknownPropertyHook';
+import assign from 'shared/assign';
 import hasOwnProperty from 'shared/hasOwnProperty';
 
 // Based on reading the React.Children implementation. TODO: type this somewhere?
@@ -563,7 +564,7 @@ function resolve(
         }
 
         if (partialState != null) {
-          inst.state = Object.assign({}, inst.state, partialState);
+          inst.state = assign({}, inst.state, partialState);
         }
       }
     } else {
@@ -695,9 +696,9 @@ function resolve(
             if (partialState != null) {
               if (dontMutate) {
                 dontMutate = false;
-                nextState = Object.assign({}, nextState, partialState);
+                nextState = assign({}, nextState, partialState);
               } else {
-                Object.assign(nextState, partialState);
+                assign(nextState, partialState);
               }
             }
           }
@@ -745,7 +746,7 @@ function resolve(
         }
       }
       if (childContext) {
-        context = Object.assign({}, context, childContext);
+        context = assign({}, context, childContext);
       }
     }
   }
@@ -1192,7 +1193,7 @@ class ReactDOMServerRenderer {
             const nextChildren = [
               React.createElement(
                 elementType.type,
-                Object.assign({ref: element.ref}, element.props),
+                assign({ref: element.ref}, element.props),
               ),
             ];
             const frame: Frame = {
@@ -1291,7 +1292,7 @@ class ReactDOMServerRenderer {
             const nextChildren = [
               React.createElement(
                 result,
-                Object.assign({ref: element.ref}, element.props),
+                assign({ref: element.ref}, element.props),
               ),
             ];
             const frame: Frame = {
@@ -1413,7 +1414,7 @@ class ReactDOMServerRenderer {
         }
       }
 
-      props = Object.assign(
+      props = assign(
         {
           type: undefined,
         },
@@ -1485,7 +1486,7 @@ class ReactDOMServerRenderer {
       if (__DEV__) {
         checkFormFieldValueStringCoercion(initialValue);
       }
-      props = Object.assign({}, props, {
+      props = assign({}, props, {
         value: undefined,
         children: '' + initialValue,
       });
@@ -1531,7 +1532,7 @@ class ReactDOMServerRenderer {
       }
       this.currentSelectValue =
         props.value != null ? props.value : props.defaultValue;
-      props = Object.assign({}, props, {
+      props = assign({}, props, {
         value: undefined,
       });
     } else if (tag === 'option') {
@@ -1577,7 +1578,7 @@ class ReactDOMServerRenderer {
           selected = '' + selectValue === value;
         }
 
-        props = Object.assign(
+        props = assign(
           {
             selected: undefined,
           },
diff --git a/packages/react-dom/src/test-utils/ReactTestUtils.js b/packages/react-dom/src/test-utils/ReactTestUtils.js
index c83b072447ba7..2c89baf398a90 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtils.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtils.js
@@ -21,6 +21,7 @@ import {
   rethrowCaughtError,
   invokeGuardedCallbackAndCatchFirstError,
 } from 'shared/ReactErrorUtils';
+import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 
 // Keep in sync with ReactDOM.js:
@@ -596,7 +597,7 @@ function makeSimulator(eventType) {
     // Since we aren't using pooling, always persist the event. This will make
     // sure it's marked and won't warn when setting additional properties.
     event.persist();
-    Object.assign(event, eventData);
+    assign(event, eventData);
 
     if (directDispatchEventTypes.has(eventType)) {
       accumulateDirectDispatchesSingle(event);
diff --git a/packages/react-native-renderer/package.json b/packages/react-native-renderer/package.json
index bc5066c43ba0c..9df888773f2ca 100644
--- a/packages/react-native-renderer/package.json
+++ b/packages/react-native-renderer/package.json
@@ -8,7 +8,6 @@
     "directory": "packages/react-native-renderer"
   },
   "dependencies": {
-    "object-assign": "^4.1.1",
     "scheduler": "^0.11.0"
   },
   "peerDependencies": {
diff --git a/packages/react-native-renderer/src/legacy-events/SyntheticEvent.js b/packages/react-native-renderer/src/legacy-events/SyntheticEvent.js
index 84d39bbd603d2..9e3009d9d8d06 100644
--- a/packages/react-native-renderer/src/legacy-events/SyntheticEvent.js
+++ b/packages/react-native-renderer/src/legacy-events/SyntheticEvent.js
@@ -7,6 +7,8 @@
 
 /* eslint valid-typeof: 0 */
 
+import assign from 'shared/assign';
+
 const EVENT_POOL_SIZE = 10;
 
 /**
@@ -110,7 +112,7 @@ function SyntheticEvent(
   return this;
 }
 
-Object.assign(SyntheticEvent.prototype, {
+assign(SyntheticEvent.prototype, {
   preventDefault: function() {
     this.defaultPrevented = true;
     const event = this.nativeEvent;
@@ -236,11 +238,11 @@ SyntheticEvent.extend = function(Interface) {
   function Class() {
     return Super.apply(this, arguments);
   }
-  Object.assign(prototype, Class.prototype);
+  assign(prototype, Class.prototype);
   Class.prototype = prototype;
   Class.prototype.constructor = Class;
 
-  Class.Interface = Object.assign({}, Super.Interface, Interface);
+  Class.Interface = assign({}, Super.Interface, Interface);
   Class.extend = Super.extend;
   addEventPoolingTo(Class);
 
diff --git a/packages/react-noop-renderer/package.json b/packages/react-noop-renderer/package.json
index 22eab24f8c5a4..aae14070714c0 100644
--- a/packages/react-noop-renderer/package.json
+++ b/packages/react-noop-renderer/package.json
@@ -11,7 +11,6 @@
   },
   "license": "MIT",
   "dependencies": {
-    "object-assign": "^4.1.1",
     "react-reconciler": "*",
     "react-client": "*",
     "react-server": "*"
diff --git a/packages/react-reconciler/package.json b/packages/react-reconciler/package.json
index a6b9986adaea3..9dc5ae52bcc88 100644
--- a/packages/react-reconciler/package.json
+++ b/packages/react-reconciler/package.json
@@ -30,7 +30,6 @@
   },
   "dependencies": {
     "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1",
     "scheduler": "^0.20.1"
   },
   "browserify": {
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.new.js b/packages/react-reconciler/src/ReactFiberClassComponent.new.js
index 0279cabd519be..23bc16ecce99a 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.new.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.new.js
@@ -35,6 +35,7 @@ import {get as getInstance, set as setInstance} from 'shared/ReactInstanceMap';
 import shallowEqual from 'shared/shallowEqual';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
+import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
@@ -186,7 +187,7 @@ function applyDerivedStateFromProps(
   const memoizedState =
     partialState === null || partialState === undefined
       ? prevState
-      : Object.assign({}, prevState, partialState);
+      : assign({}, prevState, partialState);
   workInProgress.memoizedState = memoizedState;
 
   // Once the update queue is empty, persist the derived state onto the
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.old.js b/packages/react-reconciler/src/ReactFiberClassComponent.old.js
index 184993ff35b05..793156401efb7 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.old.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.old.js
@@ -35,6 +35,7 @@ import {get as getInstance, set as setInstance} from 'shared/ReactInstanceMap';
 import shallowEqual from 'shared/shallowEqual';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
+import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
@@ -186,7 +187,7 @@ function applyDerivedStateFromProps(
   const memoizedState =
     partialState === null || partialState === undefined
       ? prevState
-      : Object.assign({}, prevState, partialState);
+      : assign({}, prevState, partialState);
   workInProgress.memoizedState = memoizedState;
 
   // Once the update queue is empty, persist the derived state onto the
diff --git a/packages/react-reconciler/src/ReactFiberLazyComponent.new.js b/packages/react-reconciler/src/ReactFiberLazyComponent.new.js
index 3773f640439bf..4bf227dc5e802 100644
--- a/packages/react-reconciler/src/ReactFiberLazyComponent.new.js
+++ b/packages/react-reconciler/src/ReactFiberLazyComponent.new.js
@@ -7,10 +7,12 @@
  * @flow
  */
 
+import assign from 'shared/assign';
+
 export function resolveDefaultProps(Component: any, baseProps: Object): Object {
   if (Component && Component.defaultProps) {
     // Resolve default props. Taken from ReactElement
-    const props = Object.assign({}, baseProps);
+    const props = assign({}, baseProps);
     const defaultProps = Component.defaultProps;
     for (const propName in defaultProps) {
       if (props[propName] === undefined) {
diff --git a/packages/react-reconciler/src/ReactFiberLazyComponent.old.js b/packages/react-reconciler/src/ReactFiberLazyComponent.old.js
index 3773f640439bf..4bf227dc5e802 100644
--- a/packages/react-reconciler/src/ReactFiberLazyComponent.old.js
+++ b/packages/react-reconciler/src/ReactFiberLazyComponent.old.js
@@ -7,10 +7,12 @@
  * @flow
  */
 
+import assign from 'shared/assign';
+
 export function resolveDefaultProps(Component: any, baseProps: Object): Object {
   if (Component && Component.defaultProps) {
     // Resolve default props. Taken from ReactElement
-    const props = Object.assign({}, baseProps);
+    const props = assign({}, baseProps);
     const defaultProps = Component.defaultProps;
     for (const propName in defaultProps) {
       if (props[propName] === undefined) {
diff --git a/packages/react-reconciler/src/ReactUpdateQueue.new.js b/packages/react-reconciler/src/ReactUpdateQueue.new.js
index c9a980890a0ad..1f665a88dfa49 100644
--- a/packages/react-reconciler/src/ReactUpdateQueue.new.js
+++ b/packages/react-reconciler/src/ReactUpdateQueue.new.js
@@ -112,6 +112,8 @@ import {
 import {pushInterleavedQueue} from './ReactFiberInterleavedUpdates.new';
 import {setIsStrictModeForDevtools} from './ReactFiberDevToolsHook.new';
 
+import assign from 'shared/assign';
+
 export type Update<State> = {|
   // TODO: Temporary field. Will remove this by storing a map of
   // transition -> event time on the root.
@@ -442,7 +444,7 @@ function getStateFromUpdate<State>(
         return prevState;
       }
       // Merge the partial state and the previous state.
-      return Object.assign({}, prevState, partialState);
+      return assign({}, prevState, partialState);
     }
     case ForceUpdate: {
       hasForceUpdate = true;
diff --git a/packages/react-reconciler/src/ReactUpdateQueue.old.js b/packages/react-reconciler/src/ReactUpdateQueue.old.js
index 9ef09b17efd10..e59ea26f2161a 100644
--- a/packages/react-reconciler/src/ReactUpdateQueue.old.js
+++ b/packages/react-reconciler/src/ReactUpdateQueue.old.js
@@ -112,6 +112,8 @@ import {
 import {pushInterleavedQueue} from './ReactFiberInterleavedUpdates.old';
 import {setIsStrictModeForDevtools} from './ReactFiberDevToolsHook.old';
 
+import assign from 'shared/assign';
+
 export type Update<State> = {|
   // TODO: Temporary field. Will remove this by storing a map of
   // transition -> event time on the root.
@@ -442,7 +444,7 @@ function getStateFromUpdate<State>(
         return prevState;
       }
       // Merge the partial state and the previous state.
-      return Object.assign({}, prevState, partialState);
+      return assign({}, prevState, partialState);
     }
     case ForceUpdate: {
       hasForceUpdate = true;
diff --git a/packages/react-server-dom-relay/package.json b/packages/react-server-dom-relay/package.json
index eeceab0da3e04..793363bb30ddc 100644
--- a/packages/react-server-dom-relay/package.json
+++ b/packages/react-server-dom-relay/package.json
@@ -8,7 +8,6 @@
     "directory": "packages/react-server-dom-relay"
   },
   "dependencies": {
-    "object-assign": "^4.1.1",
     "scheduler": "^0.11.0"
   },
   "peerDependencies": {
diff --git a/packages/react-server-dom-webpack/package.json b/packages/react-server-dom-webpack/package.json
index af705d975db70..ababa89250e3c 100644
--- a/packages/react-server-dom-webpack/package.json
+++ b/packages/react-server-dom-webpack/package.json
@@ -54,8 +54,7 @@
   "dependencies": {
     "acorn": "^6.2.1",
     "neo-async": "^2.6.1",
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1"
+    "loose-envify": "^1.1.0"
   },
   "browserify": {
     "transform": [
diff --git a/packages/react-server-native-relay/package.json b/packages/react-server-native-relay/package.json
index 1c328bd2ba32f..241913f91e6a7 100644
--- a/packages/react-server-native-relay/package.json
+++ b/packages/react-server-native-relay/package.json
@@ -8,7 +8,6 @@
     "directory": "packages/react-server-native-relay"
   },
   "dependencies": {
-    "object-assign": "^4.1.1",
     "scheduler": "^0.11.0"
   },
   "peerDependencies": {
diff --git a/packages/react-server/package.json b/packages/react-server/package.json
index 3e9252d2615d7..8c5c312a693ac 100644
--- a/packages/react-server/package.json
+++ b/packages/react-server/package.json
@@ -29,8 +29,7 @@
     "react": "^17.0.0"
   },
   "dependencies": {
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1"
+    "loose-envify": "^1.1.0"
   },
   "browserify": {
     "transform": [
diff --git a/packages/react-server/src/ReactFizzClassComponent.js b/packages/react-server/src/ReactFizzClassComponent.js
index 2e085c3f1a711..12fbeb46f2ded 100644
--- a/packages/react-server/src/ReactFizzClassComponent.js
+++ b/packages/react-server/src/ReactFizzClassComponent.js
@@ -17,6 +17,7 @@ import {
 import {get as getInstance, set as setInstance} from 'shared/ReactInstanceMap';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
+import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 
 const didWarnAboutNoopUpdateForComponent = {};
@@ -161,7 +162,7 @@ function applyDerivedStateFromProps(
   const newState =
     partialState === null || partialState === undefined
       ? prevState
-      : Object.assign({}, prevState, partialState);
+      : assign({}, prevState, partialState);
   return newState;
 }
 
@@ -602,9 +603,9 @@ function processUpdateQueue(
         if (partialState != null) {
           if (dontMutate) {
             dontMutate = false;
-            nextState = Object.assign({}, nextState, partialState);
+            nextState = assign({}, nextState, partialState);
           } else {
-            Object.assign(nextState, partialState);
+            assign(nextState, partialState);
           }
         }
       }
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index bdf9b16a2458f..a7f5ad8346939 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -117,6 +117,7 @@ import {
   enableSuspenseAvoidThisFallbackFizz,
 } from 'shared/ReactFeatureFlags';
 
+import assign from 'shared/assign';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import isArray from 'shared/isArray';
 
@@ -837,7 +838,7 @@ function validateFunctionComponentInDev(Component: any): void {
 function resolveDefaultProps(Component: any, baseProps: Object): Object {
   if (Component && Component.defaultProps) {
     // Resolve default props. Taken from ReactElement
-    const props = Object.assign({}, baseProps);
+    const props = assign({}, baseProps);
     const defaultProps = Component.defaultProps;
     for (const propName in defaultProps) {
       if (props[propName] === undefined) {
diff --git a/packages/react-test-renderer/package.json b/packages/react-test-renderer/package.json
index 26e0337641827..814e6b3d264bd 100644
--- a/packages/react-test-renderer/package.json
+++ b/packages/react-test-renderer/package.json
@@ -19,7 +19,6 @@
   },
   "homepage": "https://reactjs.org/",
   "dependencies": {
-    "object-assign": "^4.1.1",
     "react-is": "^17.0.3",
     "react-shallow-renderer": "^16.13.1",
     "scheduler": "^0.20.1"
diff --git a/packages/react/package.json b/packages/react/package.json
index 94703e2005102..9d19b02b3202b 100644
--- a/packages/react/package.json
+++ b/packages/react/package.json
@@ -38,8 +38,7 @@
     "node": ">=0.10.0"
   },
   "dependencies": {
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1"
+    "loose-envify": "^1.1.0"
   },
   "browserify": {
     "transform": [
diff --git a/packages/react/src/ReactBaseClasses.js b/packages/react/src/ReactBaseClasses.js
index e2a004bcc0467..23b8f126146dc 100644
--- a/packages/react/src/ReactBaseClasses.js
+++ b/packages/react/src/ReactBaseClasses.js
@@ -6,6 +6,7 @@
  */
 
 import ReactNoopUpdateQueue from './ReactNoopUpdateQueue';
+import assign from 'shared/assign';
 
 const emptyObject = {};
 if (__DEV__) {
@@ -139,7 +140,7 @@ function PureComponent(props, context, updater) {
 const pureComponentPrototype = (PureComponent.prototype = new ComponentDummy());
 pureComponentPrototype.constructor = PureComponent;
 // Avoid an extra prototype jump for these methods.
-Object.assign(pureComponentPrototype, Component.prototype);
+assign(pureComponentPrototype, Component.prototype);
 pureComponentPrototype.isPureReactComponent = true;
 
 export {Component, PureComponent};
diff --git a/packages/react/src/ReactElement.js b/packages/react/src/ReactElement.js
index e87f31d1ae36c..4af5a8bafb5ae 100644
--- a/packages/react/src/ReactElement.js
+++ b/packages/react/src/ReactElement.js
@@ -7,6 +7,7 @@
 
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import {REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
+import assign from 'shared/assign';
 import hasOwnProperty from 'shared/hasOwnProperty';
 import {checkKeyStringCoercion} from 'shared/CheckStringCoercion';
 
@@ -492,7 +493,7 @@ export function cloneElement(element, config, children) {
   let propName;
 
   // Original props are copied
-  const props = Object.assign({}, element.props);
+  const props = assign({}, element.props);
 
   // Reserved names are extracted
   let key = element.key;
diff --git a/packages/react/src/ReactSharedInternals.js b/packages/react/src/ReactSharedInternals.js
index 3443fb276633c..2874b03985b9e 100644
--- a/packages/react/src/ReactSharedInternals.js
+++ b/packages/react/src/ReactSharedInternals.js
@@ -5,7 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import assign from 'object-assign';
 import ReactCurrentDispatcher from './ReactCurrentDispatcher';
 import ReactCurrentBatchConfig from './ReactCurrentBatchConfig';
 import ReactCurrentActQueue from './ReactCurrentActQueue';
@@ -16,8 +15,6 @@ const ReactSharedInternals = {
   ReactCurrentDispatcher,
   ReactCurrentBatchConfig,
   ReactCurrentOwner,
-  // Used by renderers to avoid bundling object-assign twice in UMD bundles:
-  assign,
 };
 
 if (__DEV__) {
diff --git a/packages/react/src/forks/ReactSharedInternals.umd.js b/packages/react/src/forks/ReactSharedInternals.umd.js
index 5dcfbb5650e63..04e8cb577f7ab 100644
--- a/packages/react/src/forks/ReactSharedInternals.umd.js
+++ b/packages/react/src/forks/ReactSharedInternals.umd.js
@@ -5,7 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import assign from 'object-assign';
 import * as Scheduler from 'scheduler';
 import ReactCurrentDispatcher from '../ReactCurrentDispatcher';
 import ReactCurrentActQueue from '../ReactCurrentActQueue';
@@ -17,8 +16,6 @@ const ReactSharedInternals = {
   ReactCurrentDispatcher,
   ReactCurrentOwner,
   ReactCurrentBatchConfig,
-  // Used by renderers to avoid bundling object-assign twice in UMD bundles:
-  assign,
 
   // Re-export the schedule API(s) for UMD bundles.
   // This avoids introducing a dependency on a new UMD global in a minor update,
diff --git a/packages/scheduler/package.json b/packages/scheduler/package.json
index 3f88ee56bbf72..50f5778a833f3 100644
--- a/packages/scheduler/package.json
+++ b/packages/scheduler/package.json
@@ -17,8 +17,7 @@
   },
   "homepage": "https://reactjs.org/",
   "dependencies": {
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.1"
+    "loose-envify": "^1.1.0"
   },
   "files": [
     "LICENSE",
diff --git a/packages/shared/forks/object-assign.umd.js b/packages/shared/assign.js
similarity index 57%
rename from packages/shared/forks/object-assign.umd.js
rename to packages/shared/assign.js
index 3e5d03c3cca85..b9666e5e8b415 100644
--- a/packages/shared/forks/object-assign.umd.js
+++ b/packages/shared/assign.js
@@ -7,8 +7,6 @@
  * @flow
  */
 
-import * as React from 'react';
+const assign = Object.assign;
 
-const ReactInternals = React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED;
-
-export default ReactInternals.assign;
+export default assign;
diff --git a/packages/shared/forks/object-assign.inline-umd.js b/packages/shared/forks/object-assign.inline-umd.js
deleted file mode 100644
index 553fa44f6b0aa..0000000000000
--- a/packages/shared/forks/object-assign.inline-umd.js
+++ /dev/null
@@ -1,31 +0,0 @@
-/**
- * Copyright 2004-present Facebook. All Rights Reserved.
- */
-
-const hasOwnProperty = Object.prototype.hasOwnProperty;
-
-const _assign = function(to, from) {
-  for (const key in from) {
-    if (hasOwnProperty.call(from, key)) {
-      to[key] = from[key];
-    }
-  }
-};
-
-export default Object.assign ||
-  function(target, sources) {
-    if (target == null) {
-      throw new TypeError('Object.assign target cannot be null or undefined');
-    }
-
-    const to = Object(target);
-
-    for (let nextIndex = 1; nextIndex < arguments.length; nextIndex++) {
-      const nextSource = arguments[nextIndex];
-      if (nextSource != null) {
-        _assign(to, Object(nextSource));
-      }
-    }
-
-    return to;
-  };
diff --git a/packages/use-subscription/package.json b/packages/use-subscription/package.json
index 0c270f5e08ee1..cad898b5f646d 100644
--- a/packages/use-subscription/package.json
+++ b/packages/use-subscription/package.json
@@ -14,9 +14,6 @@
     "cjs/"
   ],
   "license": "MIT",
-  "dependencies": {
-    "object-assign": "^4.1.1"
-  },
   "peerDependencies": {
     "react": "^16.8.0 || ^17.0.0"
   },
diff --git a/scripts/babel/transform-object-assign-require.js b/scripts/babel/transform-object-assign.js
similarity index 77%
rename from scripts/babel/transform-object-assign-require.js
rename to scripts/babel/transform-object-assign.js
index 8b43be53e700c..9b20675f39f13 100644
--- a/scripts/babel/transform-object-assign-require.js
+++ b/scripts/babel/transform-object-assign.js
@@ -14,7 +14,7 @@ module.exports = function autoImporter(babel) {
     if (state.id) {
       return state.id;
     }
-    state.id = helperModuleImports.addDefault(path, 'object-assign', {
+    state.id = helperModuleImports.addDefault(path, 'shared/assign', {
       nameHint: 'assign',
     });
     return state.id;
@@ -28,8 +28,8 @@ module.exports = function autoImporter(babel) {
 
     visitor: {
       CallExpression: function(path, file) {
-        if (file.filename.indexOf('object-assign') !== -1) {
-          // Don't replace Object.assign if we're transforming object-assign
+        if (file.filename.indexOf('shared/assign') !== -1) {
+          // Don't replace Object.assign if we're transforming shared/assign
           return;
         }
         if (path.get('callee').matchesPattern('Object.assign')) {
@@ -40,8 +40,8 @@ module.exports = function autoImporter(babel) {
       },
 
       MemberExpression: function(path, file) {
-        if (file.filename.indexOf('object-assign') !== -1) {
-          // Don't replace Object.assign if we're transforming object-assign
+        if (file.filename.indexOf('shared/assign') !== -1) {
+          // Don't replace Object.assign if we're transforming shared/assign
           return;
         }
         if (path.matchesPattern('Object.assign')) {
diff --git a/scripts/rollup/build.js b/scripts/rollup/build.js
index 48401c002b431..c42edbe7eea64 100644
--- a/scripts/rollup/build.js
+++ b/scripts/rollup/build.js
@@ -8,7 +8,6 @@ const prettier = require('rollup-plugin-prettier');
 const replace = require('rollup-plugin-replace');
 const stripBanner = require('rollup-plugin-strip-banner');
 const chalk = require('chalk');
-const path = require('path');
 const resolve = require('rollup-plugin-node-resolve');
 const fs = require('fs');
 const argv = require('minimist')(process.argv.slice(2));
@@ -127,6 +126,8 @@ const babelPlugins = [
   '@babel/plugin-transform-parameters',
   // TODO: Remove array destructuring from the source. Requires runtime.
   ['@babel/plugin-transform-destructuring', {loose: true, useBuiltIns: true}],
+  // Transform Object spread to shared/assign
+  require('../babel/transform-object-assign'),
 ];
 
 const babelToES5Plugins = [
@@ -177,22 +178,7 @@ function getBabelConfig(
     options.plugins.push(require('../error-codes/transform-error-messages'));
   }
 
-  switch (bundleType) {
-    case UMD_DEV:
-    case UMD_PROD:
-    case UMD_PROFILING:
-    case NODE_DEV:
-    case NODE_PROD:
-    case NODE_PROFILING:
-      return Object.assign({}, options, {
-        plugins: options.plugins.concat([
-          // Use object-assign polyfill in open source
-          path.resolve('./scripts/babel/transform-object-assign-require'),
-        ]),
-      });
-    default:
-      return options;
-  }
+  return options;
 }
 
 function getRollupOutputOptions(
diff --git a/scripts/rollup/forks.js b/scripts/rollup/forks.js
index eba8f0d684b69..d45c41a74268d 100644
--- a/scripts/rollup/forks.js
+++ b/scripts/rollup/forks.js
@@ -36,38 +36,6 @@ const __EXPERIMENTAL__ =
 // algorithm because 1) require.resolve doesn't work with ESM modules, and 2)
 // the behavior is easier to predict.
 const forks = Object.freeze({
-  // Optimization: for UMDs, use a version that we can inline into the React bundle.
-  // Use that from all other bundles.
-
-  // NOTE: This is hard-coded to the main entry point of the (third-party)
-  // object-assign package.
-  './node_modules/object-assign/index.js': (
-    bundleType,
-    entry,
-    dependencies
-  ) => {
-    if (
-      bundleType !== UMD_DEV &&
-      bundleType !== UMD_PROD &&
-      bundleType !== UMD_PROFILING
-    ) {
-      // It's only relevant for UMD bundles since that's where the duplication
-      // happens. Other bundles just require('object-assign') anyway.
-      return null;
-    }
-    if (entry === 'react' || entry === 'react/src/ReactSharedSubset.js') {
-      // Use the forked version that uses ES modules instead of CommonJS.
-      return './packages/shared/forks/object-assign.inline-umd.js';
-    }
-    if (dependencies.indexOf('react') === -1) {
-      // We can only apply the optimizations to bundle that depend on React
-      // because we read assign() from an object exposed on React internals.
-      return null;
-    }
-    // We can use the fork that reads the secret export!
-    return './packages/shared/forks/object-assign.umd.js';
-  },
-
   // NOTE: This is hard-coded to the main entry point of the (third-party)
   // react-shallow-renderer package.
   './node_modules/react-shallow-renderer/index.js': () => {