diff --git a/packages/react-cs-renderer/src/ReactNativeCS.js b/packages/react-cs-renderer/src/ReactNativeCS.js
index 4b87d77ffafa5..b7ed3e8b366a8 100644
--- a/packages/react-cs-renderer/src/ReactNativeCS.js
+++ b/packages/react-cs-renderer/src/ReactNativeCS.js
@@ -265,7 +265,11 @@ const ReactCS = CSStatefulComponent({
     let container = {
       pendingChild: null,
     };
-    let root = ReactNativeCSFiberRenderer.createContainer(container, false);
+    let root = ReactNativeCSFiberRenderer.createContainer(
+      container,
+      false,
+      false,
+    );
     return {root, container};
   },
   render({
diff --git a/packages/react-dom/src/__tests__/ReactDOMFiberAsync-test.internal.js b/packages/react-dom/src/__tests__/ReactDOMFiberAsync-test.internal.js
index a598cf388991c..85f13de1befce 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFiberAsync-test.internal.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFiberAsync-test.internal.js
@@ -69,26 +69,18 @@ describe('ReactDOMFiberAsync', () => {
       ReactFeatureFlags = require('shared/ReactFeatureFlags');
       container = document.createElement('div');
       ReactFeatureFlags.enableAsyncSubtreeAPI = true;
+      ReactFeatureFlags.enableCreateRoot = true;
       ReactDOM = require('react-dom');
     });
 
-    it('AsyncComponent at the root makes the entire tree async', () => {
-      ReactDOM.render(
-        <AsyncComponent>
-          <div>Hi</div>
-        </AsyncComponent>,
-        container,
-      );
+    it('createRoot makes the entire tree async', () => {
+      const root = ReactDOM.createRoot(container);
+      root.render(<div>Hi</div>);
       expect(container.textContent).toEqual('');
       jest.runAllTimers();
       expect(container.textContent).toEqual('Hi');
 
-      ReactDOM.render(
-        <AsyncComponent>
-          <div>Bye</div>
-        </AsyncComponent>,
-        container,
-      );
+      root.render(<div>Bye</div>);
       expect(container.textContent).toEqual('Hi');
       jest.runAllTimers();
       expect(container.textContent).toEqual('Bye');
@@ -104,12 +96,8 @@ describe('ReactDOMFiberAsync', () => {
         }
       }
 
-      ReactDOM.render(
-        <AsyncComponent>
-          <Component />
-        </AsyncComponent>,
-        container,
-      );
+      const root = ReactDOM.createRoot(container);
+      root.render(<Component />);
       expect(container.textContent).toEqual('');
       jest.runAllTimers();
       expect(container.textContent).toEqual('0');
diff --git a/packages/react-dom/src/__tests__/ReactDOMRoot-test.internal.js b/packages/react-dom/src/__tests__/ReactDOMRoot-test.internal.js
index fd3fd0a07bb79..a16ad96d44e78 100644
--- a/packages/react-dom/src/__tests__/ReactDOMRoot-test.internal.js
+++ b/packages/react-dom/src/__tests__/ReactDOMRoot-test.internal.js
@@ -76,14 +76,17 @@ describe('ReactDOMRoot', () => {
   it('renders children', () => {
     const root = ReactDOM.createRoot(container);
     root.render(<div>Hi</div>);
+    flush();
     expect(container.textContent).toEqual('Hi');
   });
 
   it('unmounts children', () => {
     const root = ReactDOM.createRoot(container);
     root.render(<div>Hi</div>);
+    flush();
     expect(container.textContent).toEqual('Hi');
     root.unmount();
+    flush();
     expect(container.textContent).toEqual('');
   });
 
@@ -138,6 +141,7 @@ describe('ReactDOMRoot', () => {
         <span />
       </div>,
     );
+    flush();
     if (__DEV__) {
       expect(console.error.calls.count()).toBe(0);
     }
@@ -151,6 +155,7 @@ describe('ReactDOMRoot', () => {
         <span />
       </div>,
     );
+    flush();
     if (__DEV__) {
       expect(console.error.calls.count()).toBe(1);
       expect(console.error.calls.argsFor(0)[0]).toMatch('Extra attributes');
@@ -167,6 +172,7 @@ describe('ReactDOMRoot', () => {
         <span>d</span>
       </div>,
     );
+    flush();
     expect(container.textContent).toEqual('abcd');
     root.render(
       <div>
@@ -174,6 +180,7 @@ describe('ReactDOMRoot', () => {
         <span>c</span>
       </div>,
     );
+    flush();
     expect(container.textContent).toEqual('abdc');
   });
 
diff --git a/packages/react-dom/src/client/ReactDOM.js b/packages/react-dom/src/client/ReactDOM.js
index f898bb673a418..eb093e71d273a 100644
--- a/packages/react-dom/src/client/ReactDOM.js
+++ b/packages/react-dom/src/client/ReactDOM.js
@@ -376,8 +376,8 @@ type Root = {
   _internalRoot: FiberRoot,
 };
 
-function ReactRoot(container: Container, hydrate: boolean) {
-  const root = DOMRenderer.createContainer(container, hydrate);
+function ReactRoot(container: Container, isAsync: boolean, hydrate: boolean) {
+  const root = DOMRenderer.createContainer(container, isAsync, hydrate);
   this._internalRoot = root;
 }
 ReactRoot.prototype.render = function(
@@ -1031,8 +1031,9 @@ function legacyCreateRootFromDOMContainer(
       );
     }
   }
-  const root: Root = new ReactRoot(container, shouldHydrate);
-  return root;
+  // Legacy roots are not async by default.
+  const isAsync = false;
+  return new ReactRoot(container, isAsync, shouldHydrate);
 }
 
 function legacyRenderSubtreeIntoContainer(
@@ -1300,7 +1301,7 @@ if (enableCreateRoot) {
     options?: RootOptions,
   ): ReactRoot {
     const hydrate = options != null && options.hydrate === true;
-    return new ReactRoot(container, hydrate);
+    return new ReactRoot(container, true, hydrate);
   };
 }
 
diff --git a/packages/react-native-renderer/src/ReactNativeRenderer.js b/packages/react-native-renderer/src/ReactNativeRenderer.js
index 792bca955f329..483a049c2c15c 100644
--- a/packages/react-native-renderer/src/ReactNativeRenderer.js
+++ b/packages/react-native-renderer/src/ReactNativeRenderer.js
@@ -48,7 +48,11 @@ const ReactNativeRenderer: ReactNativeType = {
     if (!root) {
       // TODO (bvaughn): If we decide to keep the wrapper component,
       // We could create a wrapper for containerTag as well to reduce special casing.
-      root = ReactNativeFiberRenderer.createContainer(containerTag, false);
+      root = ReactNativeFiberRenderer.createContainer(
+        containerTag,
+        false,
+        false,
+      );
       roots.set(containerTag, root);
     }
     ReactNativeFiberRenderer.updateContainer(element, root, null, callback);
diff --git a/packages/react-noop-renderer/src/ReactNoop.js b/packages/react-noop-renderer/src/ReactNoop.js
index ab778ddbce658..f84e01d42c3fd 100644
--- a/packages/react-noop-renderer/src/ReactNoop.js
+++ b/packages/react-noop-renderer/src/ReactNoop.js
@@ -341,7 +341,7 @@ var ReactNoop = {
     if (!root) {
       const container = {rootID: rootID, children: []};
       rootContainers.set(rootID, container);
-      root = NoopRenderer.createContainer(container, false);
+      root = NoopRenderer.createContainer(container, true, false);
       roots.set(rootID, root);
     }
     NoopRenderer.updateContainer(element, root, null, callback);
@@ -361,7 +361,7 @@ var ReactNoop = {
     if (!root) {
       const container = {rootID: rootID, children: []};
       rootContainers.set(rootID, container);
-      root = PersistentNoopRenderer.createContainer(container, false);
+      root = PersistentNoopRenderer.createContainer(container, true, false);
       persistentRoots.set(rootID, root);
     }
     PersistentNoopRenderer.updateContainer(element, root, null, callback);
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index 257dcd65a2442..7d19081d36b64 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -35,7 +35,7 @@ import {
 import getComponentName from 'shared/getComponentName';
 
 import {NoWork} from './ReactFiberExpirationTime';
-import {NoContext} from './ReactTypeOfInternalContext';
+import {NoContext, AsyncUpdates} from './ReactTypeOfInternalContext';
 
 if (__DEV__) {
   var hasBadMapPolyfill = false;
@@ -288,9 +288,9 @@ export function createWorkInProgress(
   return workInProgress;
 }
 
-export function createHostRootFiber(): Fiber {
-  const fiber = createFiber(HostRoot, null, NoContext);
-  return fiber;
+export function createHostRootFiber(isAsync): Fiber {
+  const internalContextTag = isAsync ? AsyncUpdates : NoContext;
+  return createFiber(HostRoot, null, null, internalContextTag);
 }
 
 export function createFiberFromElement(
diff --git a/packages/react-reconciler/src/ReactFiberReconciler.js b/packages/react-reconciler/src/ReactFiberReconciler.js
index dac06f0dd1e14..b5b319047f423 100644
--- a/packages/react-reconciler/src/ReactFiberReconciler.js
+++ b/packages/react-reconciler/src/ReactFiberReconciler.js
@@ -12,7 +12,6 @@ import type {FiberRoot} from './ReactFiberRoot';
 import type {ReactNodeList} from 'shared/ReactTypes';
 import type {ExpirationTime} from './ReactFiberExpirationTime';
 
-import {enableAsyncSubtreeAPI} from 'shared/ReactFeatureFlags';
 import {
   findCurrentHostFiber,
   findCurrentHostFiberWithNoPortals,
@@ -233,7 +232,11 @@ type DevToolsConfig<I, TI> = {|
 |};
 
 export type Reconciler<C, I, TI> = {
-  createContainer(containerInfo: C, hydrate: boolean): OpaqueRoot,
+  createContainer(
+    containerInfo: C,
+    isAsync: boolean,
+    hydrate: boolean,
+  ): OpaqueRoot,
   updateContainer(
     element: ReactNodeList,
     container: OpaqueRoot,
@@ -288,7 +291,6 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
   const {getPublicInstance} = config;
 
   const {
-    computeAsyncExpiration,
     computeUniqueAsyncExpiration,
     computeExpirationForFiber,
     scheduleWork,
@@ -300,25 +302,6 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
     deferredUpdates,
   } = ReactFiberScheduler(config);
 
-  function computeRootExpirationTime(current, element) {
-    let expirationTime;
-    // Check if the top-level element is an async wrapper component. If so,
-    // treat updates to the root as async. This is a bit weird but lets us
-    // avoid a separate `renderAsync` API.
-    if (
-      enableAsyncSubtreeAPI &&
-      element != null &&
-      (element: any).type != null &&
-      (element: any).type.prototype != null &&
-      (element: any).type.prototype.unstable_isAsyncReactComponent === true
-    ) {
-      expirationTime = computeAsyncExpiration();
-    } else {
-      expirationTime = computeExpirationForFiber(current);
-    }
-    return expirationTime;
-  }
-
   function scheduleRootUpdate(
     current: Fiber,
     element: ReactNodeList,
@@ -408,8 +391,12 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
   }
 
   return {
-    createContainer(containerInfo: C, hydrate: boolean): OpaqueRoot {
-      return createFiberRoot(containerInfo, hydrate);
+    createContainer(
+      containerInfo: C,
+      isAsync: boolean,
+      hydrate: boolean,
+    ): OpaqueRoot {
+      return createFiberRoot(containerInfo, isAsync, hydrate);
     },
 
     updateContainer(
@@ -419,7 +406,7 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
       callback: ?Function,
     ): ExpirationTime {
       const current = container.current;
-      const expirationTime = computeRootExpirationTime(current, element);
+      const expirationTime = computeExpirationForFiber(current);
       return updateContainerAtExpirationTime(
         element,
         container,
diff --git a/packages/react-reconciler/src/ReactFiberRoot.js b/packages/react-reconciler/src/ReactFiberRoot.js
index b6e21ed6872e8..1dd87cc14b3e4 100644
--- a/packages/react-reconciler/src/ReactFiberRoot.js
+++ b/packages/react-reconciler/src/ReactFiberRoot.js
@@ -52,11 +52,12 @@ export type FiberRoot = {
 
 export function createFiberRoot(
   containerInfo: any,
+  isAsync: boolean,
   hydrate: boolean,
 ): FiberRoot {
   // Cyclic construction. This cheats the type system right now because
   // stateNode is any.
-  const uninitializedFiber = createHostRootFiber();
+  const uninitializedFiber = createHostRootFiber(isAsync);
   const root = {
     current: uninitializedFiber,
     containerInfo: containerInfo,
diff --git a/packages/react-reconciler/src/ReactFiberScheduler.js b/packages/react-reconciler/src/ReactFiberScheduler.js
index c69f4bbcb3a30..1a738e9624857 100644
--- a/packages/react-reconciler/src/ReactFiberScheduler.js
+++ b/packages/react-reconciler/src/ReactFiberScheduler.js
@@ -1738,7 +1738,6 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
   }
 
   return {
-    computeAsyncExpiration,
     computeExpirationForFiber,
     scheduleWork,
     requestWork,
diff --git a/packages/react-rt-renderer/src/ReactNativeRT.js b/packages/react-rt-renderer/src/ReactNativeRT.js
index 5b72f15fdee6a..9a21c4dc0ae3a 100644
--- a/packages/react-rt-renderer/src/ReactNativeRT.js
+++ b/packages/react-rt-renderer/src/ReactNativeRT.js
@@ -40,7 +40,11 @@ const ReactNativeRTFiber: ReactNativeRTType = {
     if (!root) {
       // TODO (bvaughn): If we decide to keep the wrapper component,
       // We could create a wrapper for containerTag as well to reduce special casing.
-      root = ReactNativeRTFiberRenderer.createContainer(containerTag, false);
+      root = ReactNativeRTFiberRenderer.createContainer(
+        containerTag,
+        false,
+        false,
+      );
       roots.set(containerTag, root);
     }
     ReactNativeRTFiberRenderer.updateContainer(element, root, null, callback);
diff --git a/packages/react-test-renderer/src/ReactTestRenderer.js b/packages/react-test-renderer/src/ReactTestRenderer.js
index 24cd1f4bc5129..2cb3d9eecb67c 100644
--- a/packages/react-test-renderer/src/ReactTestRenderer.js
+++ b/packages/react-test-renderer/src/ReactTestRenderer.js
@@ -572,7 +572,11 @@ const ReactTestRendererFiber = {
       createNodeMock,
       tag: 'CONTAINER',
     };
-    let root: FiberRoot | null = TestRenderer.createContainer(container, false);
+    let root: FiberRoot | null = TestRenderer.createContainer(
+      container,
+      false,
+      false,
+    );
     invariant(root != null, 'something went wrong');
     TestRenderer.updateContainer(element, root, null, null);