From 0dc4e6663dc875e0f734b1a96b26ebc33902323a Mon Sep 17 00:00:00 2001
From: Andrew Clark <git@andrewclark.io>
Date: Wed, 20 Apr 2022 14:09:11 -0400
Subject: [PATCH] Land enableClientRenderFallbackOnHydrationMismatch (#24410)

This flag is already enabled on all relevant surfaces. We can remove it.
---
 .../src/__tests__/ReactDOMFizzServer-test.js  | 113 ++----
 ...actDOMFizzSuppressHydrationWarning-test.js | 205 ++++------
 .../__tests__/ReactDOMHydrationDiff-test.js   | 381 ++----------------
 ...DOMServerPartialHydration-test.internal.js |  49 +--
 .../src/client/ReactDOMHostConfig.js          |  16 +-
 .../src/ReactFiberCompleteWork.new.js         |   2 -
 .../src/ReactFiberCompleteWork.old.js         |   2 -
 .../src/ReactFiberHydrationContext.new.js     |   2 -
 .../src/ReactFiberHydrationContext.old.js     |   2 -
 .../useMutableSourceHydration-test.js         |   2 +-
 packages/shared/ReactFeatureFlags.js          |   1 -
 .../forks/ReactFeatureFlags.native-fb.js      |   1 -
 .../forks/ReactFeatureFlags.native-oss.js     |   1 -
 .../forks/ReactFeatureFlags.test-renderer.js  |   1 -
 .../ReactFeatureFlags.test-renderer.native.js |   1 -
 .../ReactFeatureFlags.test-renderer.www.js    |   1 -
 .../shared/forks/ReactFeatureFlags.testing.js |   1 -
 .../forks/ReactFeatureFlags.testing.www.js    |   1 -
 .../forks/ReactFeatureFlags.www-dynamic.js    |   1 -
 .../shared/forks/ReactFeatureFlags.www.js     |   1 -
 20 files changed, 175 insertions(+), 609 deletions(-)

diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
index da9097c51d5e..bc609efcf0d0 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
@@ -1832,41 +1832,26 @@ describe('ReactDOMFizzServer', () => {
       },
     });
 
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        // The first paint switches to client rendering due to mismatch
-        expect(Scheduler).toFlushUntilNextPaint([
-          'client',
-          'Log recoverable error: Hydration failed because the initial ' +
-            'UI does not match what was rendered on the server.',
-          'Log recoverable error: There was an error while hydrating. ' +
-            'Because the error happened outside of a Suspense boundary, the ' +
-            'entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Warning: An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-          'Warning: Expected server HTML to contain a matching <div> in <div>.\n' +
-            '    in div (at **)\n' +
-            '    in App (at **)',
-        ],
-        {withoutStack: 1},
-      );
-      expect(getVisibleChildren(container)).toEqual(<div>client</div>);
-    } else {
-      const serverRenderedDiv = container.getElementsByTagName('div')[0];
-      // The first paint uses the server snapshot
-      expect(Scheduler).toFlushUntilNextPaint(['server']);
-      expect(getVisibleChildren(container)).toEqual(<div>server</div>);
-      // Hydration succeeded
-      expect(ref.current).toEqual(serverRenderedDiv);
-
-      // Asynchronously we detect that the store has changed on the client,
-      // and patch up the inconsistency
-      expect(Scheduler).toFlushUntilNextPaint(['client']);
-      expect(getVisibleChildren(container)).toEqual(<div>client</div>);
-      expect(ref.current).toEqual(serverRenderedDiv);
-    }
+    expect(() => {
+      // The first paint switches to client rendering due to mismatch
+      expect(Scheduler).toFlushUntilNextPaint([
+        'client',
+        'Log recoverable error: Hydration failed because the initial ' +
+          'UI does not match what was rendered on the server.',
+        'Log recoverable error: There was an error while hydrating. ' +
+          'Because the error happened outside of a Suspense boundary, the ' +
+          'entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Warning: An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+        'Warning: Expected server HTML to contain a matching <div> in <div>.\n' +
+          '    in div (at **)\n' +
+          '    in App (at **)',
+      ],
+      {withoutStack: 1},
+    );
+    expect(getVisibleChildren(container)).toEqual(<div>client</div>);
   });
 
   // The selector implementation uses the lazy ref initialization pattern
@@ -1932,43 +1917,27 @@ describe('ReactDOMFizzServer', () => {
       },
     });
 
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      // The first paint uses the client due to mismatch forcing client render
-      expect(() => {
-        // The first paint switches to client rendering due to mismatch
-        expect(Scheduler).toFlushUntilNextPaint([
-          'client',
-          'Log recoverable error: Hydration failed because the initial ' +
-            'UI does not match what was rendered on the server.',
-          'Log recoverable error: There was an error while hydrating. ' +
-            'Because the error happened outside of a Suspense boundary, the ' +
-            'entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Warning: An error occurred during hydration. The server HTML was replaced with client content',
-          'Warning: Expected server HTML to contain a matching <div> in <div>.\n' +
-            '    in div (at **)\n' +
-            '    in App (at **)',
-        ],
-        {withoutStack: 1},
-      );
-      expect(getVisibleChildren(container)).toEqual(<div>client</div>);
-    } else {
-      const serverRenderedDiv = container.getElementsByTagName('div')[0];
-
-      // The first paint uses the server snapshot
-      expect(Scheduler).toFlushUntilNextPaint(['server']);
-      expect(getVisibleChildren(container)).toEqual(<div>server</div>);
-      // Hydration succeeded
-      expect(ref.current).toEqual(serverRenderedDiv);
-
-      // Asynchronously we detect that the store has changed on the client,
-      // and patch up the inconsistency
-      expect(Scheduler).toFlushUntilNextPaint(['client']);
-      expect(getVisibleChildren(container)).toEqual(<div>client</div>);
-      expect(ref.current).toEqual(serverRenderedDiv);
-    }
+    // The first paint uses the client due to mismatch forcing client render
+    expect(() => {
+      // The first paint switches to client rendering due to mismatch
+      expect(Scheduler).toFlushUntilNextPaint([
+        'client',
+        'Log recoverable error: Hydration failed because the initial ' +
+          'UI does not match what was rendered on the server.',
+        'Log recoverable error: There was an error while hydrating. ' +
+          'Because the error happened outside of a Suspense boundary, the ' +
+          'entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Warning: An error occurred during hydration. The server HTML was replaced with client content',
+        'Warning: Expected server HTML to contain a matching <div> in <div>.\n' +
+          '    in div (at **)\n' +
+          '    in App (at **)',
+      ],
+      {withoutStack: 1},
+    );
+    expect(getVisibleChildren(container)).toEqual(<div>client</div>);
   });
 
   // @gate experimental
diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzSuppressHydrationWarning-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzSuppressHydrationWarning-test.js
index 4f65ecf241c8..ac53da312729 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzSuppressHydrationWarning-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzSuppressHydrationWarning-test.js
@@ -240,23 +240,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Expected server HTML to contain a matching <span> in <span>',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Expected server HTML to contain a matching <span> in <span>',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <span>
@@ -329,23 +324,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Did not expect server HTML to contain the text node "Server" in <span>',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Did not expect server HTML to contain the text node "Server" in <span>',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <span />
@@ -383,23 +373,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Expected server HTML to contain a matching text node for "Client" in <span>.',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Expected server HTML to contain a matching text node for "Client" in <span>.',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <span>
@@ -440,23 +425,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Did not expect server HTML to contain the text node "Server" in <span>.',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Did not expect server HTML to contain the text node "Server" in <span>.',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <span>
@@ -495,24 +475,19 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Expected server HTML to contain a matching text node for "Client" in <span>.',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Expected server HTML to contain a matching text node for "Client" in <span>.',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <span>
@@ -627,23 +602,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Expected server HTML to contain a matching <p> in <div>.',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Expected server HTML to contain a matching <p> in <div>.',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <p>Client and server</p>
@@ -679,23 +649,18 @@ describe('ReactDOMFizzServerHydrationWarning', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(() => {
-        expect(Scheduler).toFlushAndYield([
-          'Hydration failed because the initial UI does not match what was rendered on the server.',
-          'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
-        ]);
-      }).toErrorDev(
-        [
-          'Did not expect server HTML to contain a <p> in <div>.',
-          'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
-        ],
-        {withoutStack: 1},
-      );
-    } else {
-      // This used to not warn.
-      expect(Scheduler).toFlushAndYield([]);
-    }
+    expect(() => {
+      expect(Scheduler).toFlushAndYield([
+        'Hydration failed because the initial UI does not match what was rendered on the server.',
+        'There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.',
+      ]);
+    }).toErrorDev(
+      [
+        'Did not expect server HTML to contain a <p> in <div>.',
+        'An error occurred during hydration. The server HTML was replaced with client content in <div>.',
+      ],
+      {withoutStack: 1},
+    );
     expect(getVisibleChildren(container)).toEqual(
       <div>
         <p>Client and server</p>
diff --git a/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js b/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
index a6a1a9989038..9237493c6dce 100644
--- a/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
@@ -83,7 +83,7 @@ describe('ReactDOMServerHydration', () => {
           </div>
         );
       }
-      if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
+      if (gate(flags => flags.enableClientRenderFallbackOnTextMismatch)) {
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
             "Warning: Text content did not match. Server: \\"server\\" Client: \\"client\\"
@@ -262,10 +262,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <main> in <div>.
                 in main (at **)
@@ -276,16 +273,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <main> in <div>.
-                in main (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -299,10 +286,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <header> in <div>.
                 in header (at **)
@@ -313,16 +297,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <header> in <div>.
-                in header (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -336,10 +310,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <main> in <div>.
                 in main (at **)
@@ -350,16 +321,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <main> in <div>.
-                in main (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -373,10 +334,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <footer> in <div>.
                 in footer (at **)
@@ -387,16 +345,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <footer> in <div>.
-                in footer (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
     });
 
@@ -406,9 +354,7 @@ describe('ReactDOMServerHydration', () => {
         function Mismatch({isClient}) {
           return <div className="parent">{isClient && 'only'}</div>;
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
+        if (gate(flags => flags.enableClientRenderFallbackOnTextMismatch)) {
           expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Text content did not match. Server: \\"\\" Client: \\"only\\"
@@ -441,10 +387,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching text node for \\"second\\" in <div>.
                 in div (at **)
@@ -454,15 +397,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching text node for \\"second\\" in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -476,10 +410,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching text node for \\"first\\" in <div>.
                 in div (at **)
@@ -489,15 +420,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching text node for \\"first\\" in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -511,10 +433,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching text node for \\"third\\" in <div>.
                 in div (at **)
@@ -524,15 +443,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching text node for \\"third\\" in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
     });
   });
@@ -548,10 +458,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain a <main> in <div>.
                 in div (at **)
@@ -561,15 +468,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <main> in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -583,10 +481,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <main> in <div>.
                 in main (at **)
@@ -598,16 +493,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <header> in <div>.
-                in main (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -621,10 +506,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <footer> in <div>.
                 in footer (at **)
@@ -635,16 +517,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <main> in <div>.
-                in footer (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -658,10 +530,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain a <footer> in <div>.
                 in div (at **)
@@ -671,15 +540,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <footer> in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
     });
 
@@ -689,10 +549,7 @@ describe('ReactDOMServerHydration', () => {
         function Mismatch({isClient}) {
           return <div className="parent">{!isClient && 'only'}</div>;
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain the text node \\"only\\" in <div>.
                 in div (at **)
@@ -702,15 +559,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain the text node \\"only\\" in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -724,10 +572,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <main> in <div>.
                 in main (at **)
@@ -739,16 +584,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain the text node \\"first\\" in <div>.
-                in main (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -762,10 +597,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <footer> in <div>.
                 in footer (at **)
@@ -776,16 +608,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain the text node \\"second\\" in <div>.
-                in footer (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -799,10 +621,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain the text node \\"third\\" in <div>.
                 in div (at **)
@@ -812,15 +631,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain the text node \\"third\\" in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
     });
   });
@@ -844,20 +654,14 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          // TODO: This message doesn't seem to have any useful details.
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        // TODO: This message doesn't seem to have any useful details.
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: An error occurred during hydration. The server HTML was replaced with client content in <div>.",
               "Caught [Hydration failed because the initial UI does not match what was rendered on the server.]",
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        }
       });
 
       // @gate __DEV__
@@ -873,10 +677,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain a <main> in <div>.
                 in div (at **)
@@ -886,15 +687,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <main> in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -911,20 +703,14 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          // TODO: This message doesn't seem to have any useful details.
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        // TODO: This message doesn't seem to have any useful details.
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: An error occurred during hydration. The server HTML was replaced with client content in <div>.",
               "Caught [Hydration failed because the initial UI does not match what was rendered on the server.]",
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        }
       });
 
       // @gate __DEV__
@@ -941,10 +727,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain a <p> in <div>.
                 in div (at **)
@@ -954,15 +737,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <p> in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -978,10 +752,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <main> in <div>.
                 in main (at **)
@@ -992,17 +763,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating this Suspense boundary. Switched to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <main> in <div>.
-                in main (at **)
-                in Suspense (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -1018,10 +778,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <footer> in <div>.
                 in footer (at **)
@@ -1032,17 +789,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating this Suspense boundary. Switched to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <main> in <div>.
-                in footer (at **)
-                in Suspense (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -1063,14 +809,8 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          // There is no error because we don't actually hydrate fallbacks.
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        }
+        // There is no error because we don't actually hydrate fallbacks.
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
       });
 
       // @gate __DEV__
@@ -1091,14 +831,8 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          // There is no error because we don't actually hydrate fallbacks.
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
-        }
+        // There is no error because we don't actually hydrate fallbacks.
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`Array []`);
       });
     });
 
@@ -1118,10 +852,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Expected server HTML to contain a matching <header> in <div>.
                 in header (at **)
@@ -1134,16 +865,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Expected server HTML to contain a matching <header> in <div>.
-                in header (at **)
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
 
       // @gate __DEV__
@@ -1161,10 +882,7 @@ describe('ReactDOMServerHydration', () => {
             </div>
           );
         }
-        if (
-          gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)
-        ) {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
             Array [
               "Warning: Did not expect server HTML to contain a <header> in <div>.
                 in div (at **)
@@ -1174,15 +892,6 @@ describe('ReactDOMServerHydration', () => {
               "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
             ]
           `);
-        } else {
-          expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-            Array [
-              "Warning: Did not expect server HTML to contain a <header> in <div>.
-                in div (at **)
-                in Mismatch (at **)",
-            ]
-          `);
-        }
       });
     });
   });
@@ -1222,8 +931,7 @@ describe('ReactDOMServerHydration', () => {
         );
       }
 
-      if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+      expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
             "Warning: Expected server HTML to contain a matching <footer> in <div>.
               in footer (at **)
@@ -1236,18 +944,6 @@ describe('ReactDOMServerHydration', () => {
             "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
           ]
         `);
-      } else {
-        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-          Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
-              in footer (at **)
-              in Panel (at **)
-              in div (at **)
-              in ProfileSettings (at **)
-              in Mismatch (at **)",
-          ]
-        `);
-      }
     });
 
     // @gate __DEV__
@@ -1284,8 +980,7 @@ describe('ReactDOMServerHydration', () => {
         );
       }
 
-      if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
+      expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
             "Warning: Did not expect server HTML to contain a <footer> in <div>.
               in div (at **)
@@ -1296,16 +991,6 @@ describe('ReactDOMServerHydration', () => {
             "Caught [There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.]",
           ]
         `);
-      } else {
-        expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
-          Array [
-            "Warning: Did not expect server HTML to contain a <footer> in <div>.
-              in div (at **)
-              in ProfileSettings (at **)
-              in Mismatch (at **)",
-          ]
-        `);
-      }
     });
   });
 });
diff --git a/packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js b/packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js
index 19846522ee44..4fce6008bcf5 100644
--- a/packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js
+++ b/packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js
@@ -224,16 +224,7 @@ describe('ReactDOMServerPartialHydration', () => {
         Scheduler.unstable_yieldValue(error.message);
       },
     });
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      Scheduler.unstable_flushAll();
-    } else {
-      expect(() => {
-        Scheduler.unstable_flushAll();
-      }).toErrorDev(
-        // TODO: This error should not be logged in this case. It's a false positive.
-        'Did not expect server HTML to contain the text node "Hello" in <div>.',
-      );
-    }
+    Scheduler.unstable_flushAll();
     jest.runAllTimers();
 
     // Expect the server-generated HTML to stay intact.
@@ -249,7 +240,6 @@ describe('ReactDOMServerPartialHydration', () => {
     expect(container.textContent).toBe('HelloHello');
   });
 
-  // @gate enableClientRenderFallbackOnHydrationMismatch
   it('falls back to client rendering boundary on mismatch', async () => {
     // We can't use the toErrorDev helper here because this is async.
     const originalConsoleError = console.error;
@@ -532,15 +522,11 @@ describe('ReactDOMServerPartialHydration', () => {
     expect(container.innerHTML).toContain('<span>A</span>');
     expect(container.innerHTML).not.toContain('<span>B</span>');
 
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(Scheduler).toHaveYielded([
-        'There was an error while hydrating this Suspense boundary. ' +
-          'Switched to client rendering.',
-      ]);
-      expect(ref.current).not.toBe(span);
-    } else {
-      expect(ref.current).toBe(span);
-    }
+    expect(Scheduler).toHaveYielded([
+      'There was an error while hydrating this Suspense boundary. ' +
+        'Switched to client rendering.',
+    ]);
+    expect(ref.current).not.toBe(span);
   });
 
   it('recovers with client render when server rendered additional nodes at suspense root after unsuspending', async () => {
@@ -603,11 +589,7 @@ describe('ReactDOMServerPartialHydration', () => {
 
       expect(container.innerHTML).toContain('<span>A</span>');
       expect(container.innerHTML).not.toContain('<span>B</span>');
-      if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-        expect(ref.current).not.toBe(span);
-      } else {
-        expect(ref.current).toBe(span);
-      }
+      expect(ref.current).not.toBe(span);
       if (__DEV__) {
         expect(mockError).toHaveBeenCalledWith(
           'Warning: Did not expect server HTML to contain a <%s> in <%s>.%s',
@@ -660,20 +642,14 @@ describe('ReactDOMServerPartialHydration', () => {
         });
       });
     }).toErrorDev('Did not expect server HTML to contain a <span> in <div>');
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(Scheduler).toHaveYielded([
-        'Hydration failed because the initial UI does not match what was rendered on the server.',
-        'There was an error while hydrating this Suspense boundary. Switched to client rendering.',
-      ]);
-    }
+    expect(Scheduler).toHaveYielded([
+      'Hydration failed because the initial UI does not match what was rendered on the server.',
+      'There was an error while hydrating this Suspense boundary. Switched to client rendering.',
+    ]);
 
     expect(container.innerHTML).toContain('<span>A</span>');
     expect(container.innerHTML).not.toContain('<span>B</span>');
-    if (gate(flags => flags.enableClientRenderFallbackOnHydrationMismatch)) {
-      expect(ref.current).not.toBe(span);
-    } else {
-      expect(ref.current).toBe(span);
-    }
+    expect(ref.current).not.toBe(span);
   });
 
   it('calls the onDeleted hydration callback if the parent gets deleted', async () => {
@@ -3292,7 +3268,6 @@ describe('ReactDOMServerPartialHydration', () => {
 
   itHydratesWithoutMismatch('an empty string in class component', TestAppClass);
 
-  // @gate enableClientRenderFallbackOnHydrationMismatch
   it('fallback to client render on hydration mismatch at root', async () => {
     let isClient = false;
     let suspend = true;
diff --git a/packages/react-dom/src/client/ReactDOMHostConfig.js b/packages/react-dom/src/client/ReactDOMHostConfig.js
index 0cf031776399..4b640055e5b4 100644
--- a/packages/react-dom/src/client/ReactDOMHostConfig.js
+++ b/packages/react-dom/src/client/ReactDOMHostConfig.js
@@ -62,7 +62,6 @@ import dangerousStyleValue from '../shared/dangerousStyleValue';
 import {retryIfBlockedOn} from '../events/ReactDOMEventReplaying';
 
 import {
-  enableClientRenderFallbackOnHydrationMismatch,
   enableCreateEventHandleAPI,
   enableScopeAPI,
 } from 'shared/ReactFeatureFlags';
@@ -1005,10 +1004,7 @@ export function didNotHydrateInstance(
   isConcurrentMode: boolean,
 ) {
   if (__DEV__) {
-    if (
-      (enableClientRenderFallbackOnHydrationMismatch && isConcurrentMode) ||
-      parentProps[SUPPRESS_HYDRATION_WARNING] !== true
-    ) {
+    if (isConcurrentMode || parentProps[SUPPRESS_HYDRATION_WARNING] !== true) {
       if (instance.nodeType === ELEMENT_NODE) {
         warnForDeletedHydratableElement(parentInstance, (instance: any));
       } else if (instance.nodeType === COMMENT_NODE) {
@@ -1089,10 +1085,7 @@ export function didNotFindHydratableInstance(
   isConcurrentMode: boolean,
 ) {
   if (__DEV__) {
-    if (
-      (enableClientRenderFallbackOnHydrationMismatch && isConcurrentMode) ||
-      parentProps[SUPPRESS_HYDRATION_WARNING] !== true
-    ) {
+    if (isConcurrentMode || parentProps[SUPPRESS_HYDRATION_WARNING] !== true) {
       warnForInsertedHydratedElement(parentInstance, type, props);
     }
   }
@@ -1106,10 +1099,7 @@ export function didNotFindHydratableTextInstance(
   isConcurrentMode: boolean,
 ) {
   if (__DEV__) {
-    if (
-      (enableClientRenderFallbackOnHydrationMismatch && isConcurrentMode) ||
-      parentProps[SUPPRESS_HYDRATION_WARNING] !== true
-    ) {
+    if (isConcurrentMode || parentProps[SUPPRESS_HYDRATION_WARNING] !== true) {
       warnForInsertedHydratedText(parentInstance, text);
     }
   }
diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.new.js b/packages/react-reconciler/src/ReactFiberCompleteWork.new.js
index 683d29ab3c88..4cbae604140b 100644
--- a/packages/react-reconciler/src/ReactFiberCompleteWork.new.js
+++ b/packages/react-reconciler/src/ReactFiberCompleteWork.new.js
@@ -31,7 +31,6 @@ import type {SuspenseContext} from './ReactFiberSuspenseContext.new';
 import type {OffscreenState} from './ReactFiberOffscreenComponent';
 import type {Cache} from './ReactFiberCacheComponent.new';
 import {
-  enableClientRenderFallbackOnHydrationMismatch,
   enableSuspenseAvoidThisFallback,
   enableLegacyHidden,
 } from 'shared/ReactFeatureFlags';
@@ -1066,7 +1065,6 @@ function completeWork(
       const nextState: null | SuspenseState = workInProgress.memoizedState;
 
       if (
-        enableClientRenderFallbackOnHydrationMismatch &&
         hasUnhydratedTailNodes() &&
         (workInProgress.mode & ConcurrentMode) !== NoMode &&
         (workInProgress.flags & DidCapture) === NoFlags
diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.old.js b/packages/react-reconciler/src/ReactFiberCompleteWork.old.js
index 549e3da16b03..dd2703f396ee 100644
--- a/packages/react-reconciler/src/ReactFiberCompleteWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberCompleteWork.old.js
@@ -31,7 +31,6 @@ import type {SuspenseContext} from './ReactFiberSuspenseContext.old';
 import type {OffscreenState} from './ReactFiberOffscreenComponent';
 import type {Cache} from './ReactFiberCacheComponent.old';
 import {
-  enableClientRenderFallbackOnHydrationMismatch,
   enableSuspenseAvoidThisFallback,
   enableLegacyHidden,
 } from 'shared/ReactFeatureFlags';
@@ -1066,7 +1065,6 @@ function completeWork(
       const nextState: null | SuspenseState = workInProgress.memoizedState;
 
       if (
-        enableClientRenderFallbackOnHydrationMismatch &&
         hasUnhydratedTailNodes() &&
         (workInProgress.mode & ConcurrentMode) !== NoMode &&
         (workInProgress.flags & DidCapture) === NoFlags
diff --git a/packages/react-reconciler/src/ReactFiberHydrationContext.new.js b/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
index 98981e904a90..26b05d008ac5 100644
--- a/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
+++ b/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
@@ -68,7 +68,6 @@ import {
   didNotFindHydratableTextInstance,
   didNotFindHydratableSuspenseInstance,
 } from './ReactFiberHostConfig';
-import {enableClientRenderFallbackOnHydrationMismatch} from 'shared/ReactFeatureFlags';
 import {OffscreenLane} from './ReactFiberLane.new';
 import {
   getSuspendedTreeContext,
@@ -378,7 +377,6 @@ function tryHydrate(fiber, nextInstance) {
 
 function shouldClientRenderOnMismatch(fiber: Fiber) {
   return (
-    enableClientRenderFallbackOnHydrationMismatch &&
     (fiber.mode & ConcurrentMode) !== NoMode &&
     (fiber.flags & DidCapture) === NoFlags
   );
diff --git a/packages/react-reconciler/src/ReactFiberHydrationContext.old.js b/packages/react-reconciler/src/ReactFiberHydrationContext.old.js
index fd9825692784..cf7890e3edba 100644
--- a/packages/react-reconciler/src/ReactFiberHydrationContext.old.js
+++ b/packages/react-reconciler/src/ReactFiberHydrationContext.old.js
@@ -68,7 +68,6 @@ import {
   didNotFindHydratableTextInstance,
   didNotFindHydratableSuspenseInstance,
 } from './ReactFiberHostConfig';
-import {enableClientRenderFallbackOnHydrationMismatch} from 'shared/ReactFeatureFlags';
 import {OffscreenLane} from './ReactFiberLane.old';
 import {
   getSuspendedTreeContext,
@@ -378,7 +377,6 @@ function tryHydrate(fiber, nextInstance) {
 
 function shouldClientRenderOnMismatch(fiber: Fiber) {
   return (
-    enableClientRenderFallbackOnHydrationMismatch &&
     (fiber.mode & ConcurrentMode) !== NoMode &&
     (fiber.flags & DidCapture) === NoFlags
   );
diff --git a/packages/react-reconciler/src/__tests__/useMutableSourceHydration-test.js b/packages/react-reconciler/src/__tests__/useMutableSourceHydration-test.js
index cb2d7d2ac81b..a22e8114f605 100644
--- a/packages/react-reconciler/src/__tests__/useMutableSourceHydration-test.js
+++ b/packages/react-reconciler/src/__tests__/useMutableSourceHydration-test.js
@@ -169,7 +169,7 @@ describe('useMutableSourceHydration', () => {
   });
 
   // @gate enableUseMutableSource
-  // @gate enableClientRenderFallbackOnHydrationMismatch
+  // @gate enableClientRenderFallbackOnTextMismatch
   it('should detect a tear before hydrating a component', () => {
     const source = createSource('one');
     const mutableSource = createMutableSource(source, param => param.version);
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index 8f2872de99f1..218a3514f0f3 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -41,7 +41,6 @@ export const skipUnmountedBoundaries = true;
 export const enableSuspenseLayoutEffectSemantics = true;
 
 // TODO: Finish rolling out in www
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 
 // TODO: Need to review this code one more time before landing
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index 4aa7a4187f60..6baef5948997 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -50,7 +50,6 @@ export const enableSuspenseAvoidThisFallback = false;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = true;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = false;
 export const enableLegacyFBSupport = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index a210ced18e6a..e9398deee80d 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -41,7 +41,6 @@ export const enableSuspenseAvoidThisFallback = false;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = false;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = false;
 export const enableLegacyFBSupport = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index c4d6d046a3c9..c3ca7f565c73 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -41,7 +41,6 @@ export const enableSuspenseAvoidThisFallback = false;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = false;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = true;
 export const enableLegacyFBSupport = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
index aee9188ca896..d186c1852e6b 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
@@ -51,7 +51,6 @@ export const enableSuspenseAvoidThisFallback = false;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = false;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableStrictEffects = false;
 export const createRootStrictEffectsByDefault = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index 340b180dd4d7..e258b155c2c1 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -41,7 +41,6 @@ export const enableSuspenseAvoidThisFallback = true;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = false;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = true;
 export const enableLegacyFBSupport = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.testing.js b/packages/shared/forks/ReactFeatureFlags.testing.js
index 3b7013f5bacd..d173aaa1b30a 100644
--- a/packages/shared/forks/ReactFeatureFlags.testing.js
+++ b/packages/shared/forks/ReactFeatureFlags.testing.js
@@ -41,7 +41,6 @@ export const enableSuspenseAvoidThisFallback = false;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = false;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = true;
 export const enableLegacyFBSupport = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.testing.www.js b/packages/shared/forks/ReactFeatureFlags.testing.www.js
index 15e4ac5e6d6e..c2842d955938 100644
--- a/packages/shared/forks/ReactFeatureFlags.testing.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.testing.www.js
@@ -41,7 +41,6 @@ export const enableSuspenseAvoidThisFallback = true;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = true;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = true;
-export const enableClientRenderFallbackOnHydrationMismatch = true;
 export const enableClientRenderFallbackOnTextMismatch = true;
 export const enableComponentStackLocations = true;
 export const enableLegacyFBSupport = !__EXPERIMENTAL__;
diff --git a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
index cfc32d6bacff..253cb58a2d1f 100644
--- a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
+++ b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
@@ -26,7 +26,6 @@ export const enableLazyContextPropagation = __VARIANT__;
 export const enableSyncDefaultUpdates = __VARIANT__;
 export const consoleManagedByDevToolsDuringStrictMode = __VARIANT__;
 export const enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay = __VARIANT__;
-export const enableClientRenderFallbackOnHydrationMismatch = __VARIANT__;
 export const enableClientRenderFallbackOnTextMismatch = __VARIANT__;
 export const enableTransitionTracing = __VARIANT__;
 export const enableSymbolFallbackForWWW = __VARIANT__;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index 0d0fbf1a0626..5a8f89bae840 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -32,7 +32,6 @@ export const {
   enableLazyContextPropagation,
   enableSyncDefaultUpdates,
   enableCapturePhaseSelectiveHydrationWithoutDiscreteEventReplay,
-  enableClientRenderFallbackOnHydrationMismatch,
   enableClientRenderFallbackOnTextMismatch,
 } = dynamicFeatureFlags;