diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationCheckbox-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationCheckbox-test.js
index 606ec88b89893..178ed7982a44f 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationCheckbox-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationCheckbox-test.js
@@ -15,7 +15,7 @@ const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegratio
 const {disableInputAttributeSyncing} = require('shared/ReactFeatureFlags');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -23,13 +23,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationClassContextType-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationClassContextType-test.js
index dda475b7ced3e..2df2d66b9b9fa 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationClassContextType-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationClassContextType-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -21,13 +21,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationElements-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationElements-test.js
index c482010d39647..3bbdd379813e1 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationElements-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationElements-test.js
@@ -16,19 +16,23 @@ const TEXT_NODE_TYPE = 3;
 
 let React;
 let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
+let ReactFeatureFlags;
 let ReactTestUtils;
 
 function initModules() {
   jest.resetModules();
   React = require('react');
   ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
+  ReactFeatureFlags = require('shared/ReactFeatureFlags');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
@@ -136,7 +140,13 @@ describe('ReactDOMServerIntegration', () => {
         // DOM nodes on the client side. We force it to fire early
         // so that it gets deduplicated later, and doesn't fail the test.
         expect(() => {
-          ReactDOM.render(<nonstandard />, document.createElement('div'));
+          ReactDOM.flushSync(() => {
+            const root = ReactDOMClient.createRoot(
+              document.createElement('div'),
+            );
+
+            root.render(<nonstandard />);
+          });
         }).toErrorDev('The tag <nonstandard> is unrecognized in this browser.');
 
         const e = await render(<nonstandard>Text</nonstandard>);
@@ -833,15 +843,21 @@ describe('ReactDOMServerIntegration', () => {
         'an element with one text child with special characters',
         async render => {
           const e = await render(<div>{'foo\rbar\r\nbaz\nqux\u0000'}</div>);
-          if (render === serverRender || render === streamRender) {
+          if (
+            render === serverRender ||
+            render === streamRender ||
+            (render === clientRenderOnServerString &&
+              ReactFeatureFlags.enableClientRenderFallbackOnTextMismatch)
+          ) {
             expect(e.childNodes.length).toBe(1);
-            // Everything becomes LF when parsed from server HTML.
+            // Everything becomes LF when parsed from server HTML or hydrated if enableClientRenderFallbackOnTextMismatch is on.
             // Null character is ignored.
             expectNode(e.childNodes[0], TEXT_NODE_TYPE, 'foo\nbar\nbaz\nqux');
           } else {
             expect(e.childNodes.length).toBe(1);
-            // Client rendering (or hydration) uses JS value with CR.
+            // Client rendering (or hydration without enableClientRenderFallbackOnTextMismatch) uses JS value with CR.
             // Null character stays.
+
             expectNode(
               e.childNodes[0],
               TEXT_NODE_TYPE,
@@ -860,17 +876,23 @@ describe('ReactDOMServerIntegration', () => {
               {'\r\nbaz\nqux\u0000'}
             </div>,
           );
-          if (render === serverRender || render === streamRender) {
+          if (
+            render === serverRender ||
+            render === streamRender ||
+            (render === clientRenderOnServerString &&
+              ReactFeatureFlags.enableClientRenderFallbackOnTextMismatch)
+          ) {
             // We have three nodes because there is a comment between them.
             expect(e.childNodes.length).toBe(3);
-            // Everything becomes LF when parsed from server HTML.
+            // Everything becomes LF when parsed from server HTML or hydrated if enableClientRenderFallbackOnTextMismatch is on.
             // Null character is ignored.
             expectNode(e.childNodes[0], TEXT_NODE_TYPE, 'foo\nbar');
             expectNode(e.childNodes[2], TEXT_NODE_TYPE, '\nbaz\nqux');
           } else if (render === clientRenderOnServerString) {
             // We have three nodes because there is a comment between them.
             expect(e.childNodes.length).toBe(3);
-            // Hydration uses JS value with CR and null character.
+            // Hydration without enableClientRenderFallbackOnTextMismatch uses JS value with CR and null character.
+
             expectNode(e.childNodes[0], TEXT_NODE_TYPE, 'foo\rbar');
             expectNode(e.childNodes[2], TEXT_NODE_TYPE, '\r\nbaz\nqux\u0000');
           } else {
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationFragment-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationFragment-test.js
index 680f283b6dbf2..8e8fc2aa8fe27 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationFragment-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationFragment-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -21,13 +21,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationInput-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationInput-test.js
index afbbf28a41ecb..54780dae52cdb 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationInput-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationInput-test.js
@@ -15,7 +15,7 @@ const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegratio
 const {disableInputAttributeSyncing} = require('shared/ReactFeatureFlags');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -23,13 +23,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationModes-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationModes-test.js
index e551a72b9ace4..99cf33b821f17 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationModes-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationModes-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -21,13 +21,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationRefs-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationRefs-test.js
index 76da3e92c82ad..e5564d3d9348c 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationRefs-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationRefs-test.js
@@ -12,7 +12,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -20,13 +20,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationSpecialTypes-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationSpecialTypes-test.js
index f3a8b869ad818..8ea1c9d53baee 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationSpecialTypes-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationSpecialTypes-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 let forwardRef;
@@ -26,7 +26,7 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
   forwardRef = React.forwardRef;
@@ -44,7 +44,7 @@ function initModules() {
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationTextarea-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationTextarea-test.js
index 697ec7f340d88..dd19385e62c56 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationTextarea-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationTextarea-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -21,13 +21,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationUserInteraction-test.js b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationUserInteraction-test.js
index b335b03b01d38..bc5980f23dda2 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerIntegrationUserInteraction-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerIntegrationUserInteraction-test.js
@@ -12,7 +12,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -20,13 +20,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/ReactDOMserverIntegrationProgress-test.js b/packages/react-dom/src/__tests__/ReactDOMserverIntegrationProgress-test.js
index b949e0ab522f9..cf51eff4aced3 100644
--- a/packages/react-dom/src/__tests__/ReactDOMserverIntegrationProgress-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMserverIntegrationProgress-test.js
@@ -13,7 +13,7 @@
 const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegrationTestUtils');
 
 let React;
-let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
@@ -21,13 +21,13 @@ function initModules() {
   // Reset warning cache.
   jest.resetModules();
   React = require('react');
-  ReactDOM = require('react-dom');
+  ReactDOMClient = require('react-dom/client');
   ReactDOMServer = require('react-dom/server');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
   return {
-    ReactDOM,
+    ReactDOMClient,
     ReactDOMServer,
     ReactTestUtils,
   };
diff --git a/packages/react-dom/src/__tests__/utils/ReactDOMServerIntegrationTestUtils.js b/packages/react-dom/src/__tests__/utils/ReactDOMServerIntegrationTestUtils.js
index 8392b57af03cf..e9c4479b028fb 100644
--- a/packages/react-dom/src/__tests__/utils/ReactDOMServerIntegrationTestUtils.js
+++ b/packages/react-dom/src/__tests__/utils/ReactDOMServerIntegrationTestUtils.js
@@ -14,11 +14,12 @@ const shouldIgnoreConsoleError = require('../../../../../scripts/jest/shouldIgno
 
 module.exports = function (initModules) {
   let ReactDOM;
+  let ReactDOMClient;
   let ReactDOMServer;
   let act;
 
   function resetModules() {
-    ({ReactDOM, ReactDOMServer} = initModules());
+    ({ReactDOM, ReactDOMClient, ReactDOMServer} = initModules());
     act = require('internal-test-utils').act;
   }
 
@@ -51,11 +52,24 @@ module.exports = function (initModules) {
   async function asyncReactDOMRender(reactElement, domElement, forceHydrate) {
     if (forceHydrate) {
       await act(() => {
-        ReactDOM.hydrate(reactElement, domElement);
+        if (ReactDOMClient) {
+          ReactDOMClient.hydrateRoot(domElement, reactElement, {
+            onRecoverableError: () => {
+              // TODO: assert on recoverable error count.
+            },
+          });
+        } else {
+          ReactDOM.hydrate(reactElement, domElement);
+        }
       });
     } else {
       await act(() => {
-        ReactDOM.render(reactElement, domElement);
+        if (ReactDOMClient) {
+          const root = ReactDOMClient.createRoot(domElement);
+          root.render(reactElement);
+        } else {
+          ReactDOM.render(reactElement, domElement);
+        }
       });
     }
   }
@@ -80,7 +94,11 @@ module.exports = function (initModules) {
       for (let i = 0; i < console.error.mock.calls.length; i++) {
         const args = console.error.mock.calls[i];
         const [format, ...rest] = args;
-        if (!shouldIgnoreConsoleError(format, rest)) {
+        if (
+          !shouldIgnoreConsoleError(format, rest, {
+            TODO_ignoreHydrationErrors: true,
+          })
+        ) {
           filteredWarnings.push(args);
         }
       }
diff --git a/scripts/jest/shouldIgnoreConsoleError.js b/scripts/jest/shouldIgnoreConsoleError.js
index 42aae220debed..79ec7fc2ad7d6 100644
--- a/scripts/jest/shouldIgnoreConsoleError.js
+++ b/scripts/jest/shouldIgnoreConsoleError.js
@@ -1,6 +1,10 @@
 'use strict';
 
-module.exports = function shouldIgnoreConsoleError(format, args) {
+module.exports = function shouldIgnoreConsoleError(
+  format,
+  args,
+  {TODO_ignoreHydrationErrors} = {TODO_ignoreHydrationErrors: false}
+) {
   if (__DEV__) {
     if (typeof format === 'string') {
       if (format.indexOf('Error: Uncaught [') === 0) {
@@ -23,6 +27,15 @@ module.exports = function shouldIgnoreConsoleError(format, args) {
         // We haven't finished migrating our tests to use createRoot.
         return true;
       }
+      if (
+        TODO_ignoreHydrationErrors &&
+        format.indexOf(
+          'An error occurred during hydration. The server HTML was replaced with client content in'
+        ) !== -1
+      ) {
+        // This also gets logged by onRecoverableError, so we can ignore it.
+        return true;
+      }
     } else if (
       format != null &&
       typeof format.message === 'string' &&