diff --git a/packages/react-dom-bindings/src/client/ReactDOMComponent.js b/packages/react-dom-bindings/src/client/ReactDOMComponent.js
index edfb945c35fe9..a94c990733915 100644
--- a/packages/react-dom-bindings/src/client/ReactDOMComponent.js
+++ b/packages/react-dom-bindings/src/client/ReactDOMComponent.js
@@ -69,7 +69,6 @@ import {
   enableCustomElementPropertySupport,
   enableClientRenderFallbackOnTextMismatch,
   enableFormActions,
-  enableHostSingletons,
   disableIEWorkarounds,
   enableTrustedTypesIntegration,
   enableFilterEmptyStringAttributesDOM,
@@ -394,8 +393,7 @@ function setProp(
         // show within the <textarea> until it has been focused and blurred again.
         // https://github.com/facebook/react/issues/6731#issuecomment-254874553
         const canSetTextContent =
-          (!enableHostSingletons || tag !== 'body') &&
-          (tag !== 'textarea' || value !== '');
+          tag !== 'body' && (tag !== 'textarea' || value !== '');
         if (canSetTextContent) {
           setTextContent(domElement, value);
         }
@@ -403,7 +401,7 @@ function setProp(
         if (__DEV__) {
           validateTextNesting('' + value, tag);
         }
-        const canSetTextContent = !enableHostSingletons || tag !== 'body';
+        const canSetTextContent = tag !== 'body';
         if (canSetTextContent) {
           setTextContent(domElement, '' + value);
         }
@@ -2822,7 +2820,7 @@ export function diffHydratedProperties(
         // we can get away with it.
         // Host singletons get their children appended and don't use the text
         // content mechanism.
-        if (!enableHostSingletons || tag !== 'body') {
+        if (tag !== 'body') {
           domElement.textContent = (children: any);
         }
       }
diff --git a/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js b/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
index 839f346c9d88f..7007a520b88db 100644
--- a/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
+++ b/packages/react-dom-bindings/src/client/ReactDOMComponentTree.js
@@ -34,11 +34,7 @@ import {
 
 import {getParentSuspenseInstance} from './ReactFiberConfigDOM';
 
-import {
-  enableScopeAPI,
-  enableFloat,
-  enableHostSingletons,
-} from 'shared/ReactFeatureFlags';
+import {enableScopeAPI, enableFloat} from 'shared/ReactFeatureFlags';
 
 const randomKey = Math.random().toString(36).slice(2);
 const internalInstanceKey = '__reactFiber$' + randomKey;
@@ -180,7 +176,7 @@ export function getInstanceFromNode(node: Node): Fiber | null {
       tag === HostText ||
       tag === SuspenseComponent ||
       (enableFloat ? tag === HostHoistable : false) ||
-      (enableHostSingletons ? tag === HostSingleton : false) ||
+      tag === HostSingleton ||
       tag === HostRoot
     ) {
       return inst;
@@ -200,7 +196,7 @@ export function getNodeFromInstance(inst: Fiber): Instance | TextInstance {
   if (
     tag === HostComponent ||
     (enableFloat ? tag === HostHoistable : false) ||
-    (enableHostSingletons ? tag === HostSingleton : false) ||
+    tag === HostSingleton ||
     tag === HostText
   ) {
     // In Fiber this, is just the state node right now. We assume it will be
diff --git a/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js b/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
index 5a8a2ca237a8f..a83d4981d4a88 100644
--- a/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
+++ b/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
@@ -92,7 +92,6 @@ import {
   enableCreateEventHandleAPI,
   enableScopeAPI,
   enableFloat,
-  enableHostSingletons,
   enableTrustedTypesIntegration,
   enableFormActions,
   enableAsyncActions,
@@ -939,32 +938,18 @@ export function unhideTextInstance(
 }
 
 export function clearContainer(container: Container): void {
-  if (enableHostSingletons) {
-    const nodeType = container.nodeType;
-    if (nodeType === DOCUMENT_NODE) {
-      clearContainerSparingly(container);
-    } else if (nodeType === ELEMENT_NODE) {
-      switch (container.nodeName) {
-        case 'HEAD':
-        case 'HTML':
-        case 'BODY':
-          clearContainerSparingly(container);
-          return;
-        default: {
-          container.textContent = '';
-        }
-      }
-    }
-  } else {
-    if (container.nodeType === ELEMENT_NODE) {
-      // We have refined the container to Element type
-      const element: Element = (container: any);
-      element.textContent = '';
-    } else if (container.nodeType === DOCUMENT_NODE) {
-      // We have refined the container to Document type
-      const doc: Document = (container: any);
-      if (doc.documentElement) {
-        doc.removeChild(doc.documentElement);
+  const nodeType = container.nodeType;
+  if (nodeType === DOCUMENT_NODE) {
+    clearContainerSparingly(container);
+  } else if (nodeType === ELEMENT_NODE) {
+    switch (container.nodeName) {
+      case 'HEAD':
+      case 'HTML':
+      case 'BODY':
+        clearContainerSparingly(container);
+        return;
+      default: {
+        container.textContent = '';
       }
     }
   }
@@ -1053,7 +1038,7 @@ export function canHydrateInstance(
     const element: Element = (instance: any);
     const anyProps = (props: any);
     if (element.nodeName.toLowerCase() !== type.toLowerCase()) {
-      if (!inRootOrSingleton || !enableHostSingletons) {
+      if (!inRootOrSingleton) {
         // Usually we error for mismatched tags.
         if (
           enableFormActions &&
@@ -1067,7 +1052,7 @@ export function canHydrateInstance(
         }
       }
       // In root or singleton parents we skip past mismatched instances.
-    } else if (!inRootOrSingleton || !enableHostSingletons) {
+    } else if (!inRootOrSingleton) {
       // Match
       if (
         enableFormActions &&
@@ -1212,7 +1197,7 @@ export function canHydrateTextInstance(
     ) {
       // If we have extra hidden inputs, we don't mismatch. This allows us to
       // embed extra form data in the original form.
-    } else if (!inRootOrSingleton || !enableHostSingletons) {
+    } else if (!inRootOrSingleton) {
       return null;
     }
     const nextInstance = getNextHydratableSibling(instance);
@@ -1230,7 +1215,7 @@ export function canHydrateSuspenseInstance(
   inRootOrSingleton: boolean,
 ): null | SuspenseInstance {
   while (instance.nodeType !== COMMENT_NODE) {
-    if (!inRootOrSingleton || !enableHostSingletons) {
+    if (!inRootOrSingleton) {
       return null;
     }
     const nextInstance = getNextHydratableSibling(instance);
@@ -1292,7 +1277,7 @@ export function canHydrateFormStateMarker(
   inRootOrSingleton: boolean,
 ): null | FormStateMarkerInstance {
   while (instance.nodeType !== COMMENT_NODE) {
-    if (!inRootOrSingleton || !enableHostSingletons) {
+    if (!inRootOrSingleton) {
       return null;
     }
     const nextInstance = getNextHydratableSibling(instance);
@@ -1501,9 +1486,7 @@ export function shouldDeleteUnhydratedTailInstances(
   parentType: string,
 ): boolean {
   return (
-    (enableHostSingletons ||
-      (parentType !== 'head' && parentType !== 'body')) &&
-    (!enableFormActions || (parentType !== 'form' && parentType !== 'button'))
+    !enableFormActions || (parentType !== 'form' && parentType !== 'button')
   );
 }
 
diff --git a/packages/react-dom-bindings/src/events/DOMPluginEventSystem.js b/packages/react-dom-bindings/src/events/DOMPluginEventSystem.js
index 22c15a676c144..ca89e1d1bd8ab 100644
--- a/packages/react-dom-bindings/src/events/DOMPluginEventSystem.js
+++ b/packages/react-dom-bindings/src/events/DOMPluginEventSystem.js
@@ -53,7 +53,6 @@ import {
   enableCreateEventHandleAPI,
   enableScopeAPI,
   enableFloat,
-  enableHostSingletons,
   enableFormActions,
 } from 'shared/ReactFeatureFlags';
 import {
@@ -637,7 +636,7 @@ export function dispatchEventForPluginEventSystem(
               parentTag === HostComponent ||
               parentTag === HostText ||
               (enableFloat ? parentTag === HostHoistable : false) ||
-              (enableHostSingletons ? parentTag === HostSingleton : false)
+              parentTag === HostSingleton
             ) {
               node = ancestorInst = parentNode;
               continue mainLoop;
@@ -695,7 +694,7 @@ export function accumulateSinglePhaseListeners(
     if (
       (tag === HostComponent ||
         (enableFloat ? tag === HostHoistable : false) ||
-        (enableHostSingletons ? tag === HostSingleton : false)) &&
+        tag === HostSingleton) &&
       stateNode !== null
     ) {
       lastHostComponent = stateNode;
@@ -809,7 +808,7 @@ export function accumulateTwoPhaseListeners(
     if (
       (tag === HostComponent ||
         (enableFloat ? tag === HostHoistable : false) ||
-        (enableHostSingletons ? tag === HostSingleton : false)) &&
+        tag === HostSingleton) &&
       stateNode !== null
     ) {
       const currentTarget = stateNode;
@@ -843,11 +842,7 @@ function getParent(inst: Fiber | null): Fiber | null {
     // events to their parent. We could also go through parentNode on the
     // host node but that wouldn't work for React Native and doesn't let us
     // do the portal feature.
-  } while (
-    inst &&
-    inst.tag !== HostComponent &&
-    (!enableHostSingletons ? true : inst.tag !== HostSingleton)
-  );
+  } while (inst && inst.tag !== HostComponent && inst.tag !== HostSingleton);
   if (inst) {
     return inst;
   }
@@ -916,7 +911,7 @@ function accumulateEnterLeaveListenersForEvent(
     if (
       (tag === HostComponent ||
         (enableFloat ? tag === HostHoistable : false) ||
-        (enableHostSingletons ? tag === HostSingleton : false)) &&
+        tag === HostSingleton) &&
       stateNode !== null
     ) {
       const currentTarget = stateNode;
diff --git a/packages/react-dom-bindings/src/events/plugins/EnterLeaveEventPlugin.js b/packages/react-dom-bindings/src/events/plugins/EnterLeaveEventPlugin.js
index 1512f2c80d6ad..e8f08b55d955d 100644
--- a/packages/react-dom-bindings/src/events/plugins/EnterLeaveEventPlugin.js
+++ b/packages/react-dom-bindings/src/events/plugins/EnterLeaveEventPlugin.js
@@ -24,7 +24,6 @@ import {
 } from '../../client/ReactDOMComponentTree';
 import {accumulateEnterLeaveTwoPhaseListeners} from '../DOMPluginEventSystem';
 
-import {enableHostSingletons} from 'shared/ReactFeatureFlags';
 import {
   HostComponent,
   HostSingleton,
@@ -110,9 +109,7 @@ function extractEvents(
       const tag = to.tag;
       if (
         to !== nearestMounted ||
-        (tag !== HostComponent &&
-          (!enableHostSingletons ? true : tag !== HostSingleton) &&
-          tag !== HostText)
+        (tag !== HostComponent && tag !== HostSingleton && tag !== HostText)
       ) {
         to = null;
       }
diff --git a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
index 622722a947d7d..2cc4df5d779c5 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
@@ -6202,7 +6202,7 @@ body {
       );
     });
 
-    // @gate enableFloat && enableHostSingletons && enableClientRenderFallbackOnTextMismatch
+    // @gate enableFloat && enableClientRenderFallbackOnTextMismatch
     it('retains styles even when a new html, head, and/body mount', async () => {
       await act(() => {
         const {pipe} = renderToPipeableStream(
@@ -6254,58 +6254,7 @@ body {
       );
     });
 
-    // @gate enableFloat && !enableHostSingletons
-    it('retains styles even when a new html, head, and/body mount - without HostSingleton', async () => {
-      await act(() => {
-        const {pipe} = renderToPipeableStream(
-          <html>
-            <head />
-            <body>
-              <link rel="stylesheet" href="foo" precedence="foo" />
-              <link rel="stylesheet" href="bar" precedence="bar" />
-              server
-            </body>
-          </html>,
-        );
-        pipe(writable);
-      });
-      const errors = [];
-      ReactDOMClient.hydrateRoot(
-        document,
-        <html>
-          <head>
-            <link rel="stylesheet" href="qux" precedence="qux" />
-            <link rel="stylesheet" href="foo" precedence="foo" />
-          </head>
-          <body>client</body>
-        </html>,
-        {
-          onRecoverableError(error) {
-            errors.push(error.message);
-          },
-        },
-      );
-      await expect(async () => {
-        await waitForAll([]);
-      }).toErrorDev(
-        [
-          'Warning: Text content did not match. Server: "server" Client: "client"',
-          'Warning: An error occurred during hydration. The server HTML was replaced with client content in <#document>.',
-        ],
-        {withoutStack: 1},
-      );
-      expect(getMeaningfulChildren(document)).toEqual(
-        <html>
-          <head>
-            <link rel="stylesheet" href="qux" data-precedence="qux" />
-            <link rel="stylesheet" href="foo" data-precedence="foo" />
-          </head>
-          <body>client</body>
-        </html>,
-      );
-    });
-
-    // @gate enableFloat && enableHostSingletons
+    // @gate enableFloat
     it('retains styles in head through head remounts', async () => {
       const root = ReactDOMClient.createRoot(document);
       root.render(
@@ -8114,7 +8063,7 @@ background-color: green;
       ]);
     });
 
-    // @gate enableFloat && enableHostSingletons && (enableClientRenderFallbackOnTextMismatch || !__DEV__)
+    // @gate enableFloat && (enableClientRenderFallbackOnTextMismatch || !__DEV__)
     it('can render a title before a singleton even if that singleton clears its contents', async () => {
       await act(() => {
         const {pipe} = renderToPipeableStream(
diff --git a/packages/react-dom/src/__tests__/ReactDOMRoot-test.js b/packages/react-dom/src/__tests__/ReactDOMRoot-test.js
index c601691c96873..8a241135269fe 100644
--- a/packages/react-dom/src/__tests__/ReactDOMRoot-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMRoot-test.js
@@ -375,7 +375,7 @@ describe('ReactDOMRoot', () => {
     await waitForAll([]);
     container.innerHTML = '';
 
-    if (gate(flags => flags.enableFloat || flags.enableHostSingletons)) {
+    if (gate(flags => flags.enableFloat)) {
       // When either of these flags are on this validation is turned off so we
       // expect there to be no warnings
       root.render(<div>Hi</div>);
diff --git a/packages/react-dom/src/__tests__/ReactDOMSingletonComponents-test.js b/packages/react-dom/src/__tests__/ReactDOMSingletonComponents-test.js
index 7d1bddbe661c2..9c4c3fc913be1 100644
--- a/packages/react-dom/src/__tests__/ReactDOMSingletonComponents-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMSingletonComponents-test.js
@@ -123,7 +123,7 @@ describe('ReactDOM HostSingleton', () => {
       : children;
   }
 
-  // @gate enableHostSingletons && enableFloat
+  // @gate enableFloat
   it('warns if you render the same singleton twice at the same time', async () => {
     const root = ReactDOMClient.createRoot(document);
     root.render(
@@ -208,16 +208,8 @@ describe('ReactDOM HostSingleton', () => {
     );
   });
 
-  // @gate enableHostSingletons && enableFloat
+  // @gate enableFloat
   it('renders into html, head, and body persistently so the node identities never change and extraneous styles are retained', async () => {
-    gate(flags => {
-      if (flags.enableHostSingletons !== true) {
-        // We throw here because when this test fails it ends up with sync work in a microtask
-        // that throws after the expectTestToFail check asserts the failure. this causes even the
-        // expected failure to fail. This just fails explicitly and early
-        throw new Error('manually opting out of test');
-      }
-    });
     // Server render some html that will get replaced with a client render
     await actIntoEmptyDocument(() => {
       const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
@@ -601,7 +593,6 @@ describe('ReactDOM HostSingleton', () => {
   });
 
   // This test is not supported in this implementation. If we reintroduce insertion edge we should revisit
-  // @gate enableHostSingletons
   xit('is able to maintain insertions in head and body between tree-adjacent Nodes', async () => {
     // Server render some html and hydrate on the client
     await actIntoEmptyDocument(() => {
@@ -732,7 +723,6 @@ describe('ReactDOM HostSingleton', () => {
     );
   });
 
-  // @gate enableHostSingletons
   it('clears persistent head and body when html is the container', async () => {
     await actIntoEmptyDocument(() => {
       const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
@@ -785,7 +775,6 @@ describe('ReactDOM HostSingleton', () => {
     );
   });
 
-  // @gate enableHostSingletons
   it('clears persistent head when it is the container', async () => {
     await actIntoEmptyDocument(() => {
       const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
@@ -817,7 +806,7 @@ describe('ReactDOM HostSingleton', () => {
     );
   });
 
-  // @gate enableHostSingletons && enableFloat
+  // @gate enableFloat
   it('clears persistent body when it is the container', async () => {
     await actIntoEmptyDocument(() => {
       const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
@@ -974,7 +963,6 @@ describe('ReactDOM HostSingleton', () => {
     );
   });
 
-  // @gate enableHostSingletons
   it('allows for hydrating without a head', async () => {
     await actIntoEmptyDocument(() => {
       const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
diff --git a/packages/react-dom/src/__tests__/ReactMount-test.js b/packages/react-dom/src/__tests__/ReactMount-test.js
index df92131a7cb17..b679466b25a30 100644
--- a/packages/react-dom/src/__tests__/ReactMount-test.js
+++ b/packages/react-dom/src/__tests__/ReactMount-test.js
@@ -149,17 +149,8 @@ describe('ReactMount', () => {
     const iFrame = document.createElement('iframe');
     document.body.appendChild(iFrame);
 
-    if (gate(flags => flags.enableHostSingletons)) {
-      // HostSingletons make the warning for document.body unecessary
-      ReactDOM.render(<div />, iFrame.contentDocument.body);
-    } else {
-      expect(() =>
-        ReactDOM.render(<div />, iFrame.contentDocument.body),
-      ).toErrorDev(
-        'Rendering components directly into document.body is discouraged',
-        {withoutStack: true},
-      );
-    }
+    // HostSingletons make the warning for document.body unecessary
+    ReactDOM.render(<div />, iFrame.contentDocument.body);
   });
 
   it('should account for escaping on a checksum mismatch', () => {
diff --git a/packages/react-dom/src/__tests__/ReactRenderDocument-test.js b/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
index a746e5e9f0075..1ca24a5cdb39a 100644
--- a/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
+++ b/packages/react-dom/src/__tests__/ReactRenderDocument-test.js
@@ -62,7 +62,6 @@ describe('rendering React components at document', () => {
       expect(body === testDocument.body).toBe(true);
     });
 
-    // @gate enableHostSingletons
     it('should be able to unmount component from document node, but leaves singleton nodes intact', () => {
       class Root extends React.Component {
         render() {
@@ -95,31 +94,6 @@ describe('rendering React components at document', () => {
       expect(originalHead.firstChild).toEqual(null);
     });
 
-    // @gate !enableHostSingletons
-    it('should be able to unmount component from document node', () => {
-      class Root extends React.Component {
-        render() {
-          return (
-            <html>
-              <head>
-                <title>Hello World</title>
-              </head>
-              <body>Hello world</body>
-            </html>
-          );
-        }
-      }
-
-      const markup = ReactDOMServer.renderToString(<Root />);
-      const testDocument = getTestDocument(markup);
-      ReactDOM.hydrate(<Root />, testDocument);
-      expect(testDocument.body.innerHTML).toBe('Hello world');
-
-      // When we unmount everything is removed except the persistent nodes of html, head, and body
-      ReactDOM.unmountComponentAtNode(testDocument);
-      expect(testDocument.firstChild).toBe(null);
-    });
-
     it('should not be able to switch root constructors', () => {
       class Component extends React.Component {
         render() {
diff --git a/packages/react-dom/src/__tests__/validateDOMNesting-test.js b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
index ca1d921134785..da7c7f3acb96a 100644
--- a/packages/react-dom/src/__tests__/validateDOMNesting-test.js
+++ b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
@@ -38,15 +38,7 @@ function expectWarnings(tags, warnings = [], withoutStack = 0) {
 describe('validateDOMNesting', () => {
   it('allows valid nestings', () => {
     expectWarnings(['table', 'tbody', 'tr', 'td', 'b']);
-    expectWarnings(
-      ['body', 'datalist', 'option'],
-      [
-        gate(flags => !flags.enableHostSingletons)
-          ? 'render(): Rendering components directly into document.body is discouraged'
-          : null,
-      ].filter(Boolean),
-      1,
-    );
+    expectWarnings(['body', 'datalist', 'option']);
     expectWarnings(['div', 'a', 'object', 'a']);
     expectWarnings(['div', 'p', 'button', 'p']);
     expectWarnings(['p', 'svg', 'foreignObject', 'p']);
@@ -106,45 +98,22 @@ describe('validateDOMNesting', () => {
           '    in html (at **)',
       ],
     );
-    if (gate(flags => flags.enableHostSingletons)) {
-      expectWarnings(
-        ['body', 'body'],
-        [
-          'validateDOMNesting(...): <body> cannot appear as a child of <body>.\n' +
-            '    in body (at **)',
-        ],
-      );
-    } else {
-      expectWarnings(
-        ['body', 'body'],
-        [
-          'render(): Rendering components directly into document.body is discouraged',
-          'validateDOMNesting(...): <body> cannot appear as a child of <body>.\n' +
-            '    in body (at **)',
-        ],
-        1,
-      );
-    }
-    if (gate(flags => flags.enableHostSingletons)) {
-      expectWarnings(
-        ['svg', 'foreignObject', 'body', 'p'],
-        [
-          'validateDOMNesting(...): <body> cannot appear as a child of <foreignObject>.\n' +
-            '    in body (at **)\n' +
-            '    in foreignObject (at **)',
-          'Warning: You are mounting a new body component when a previous one has not first unmounted. It is an error to render more than one body component at a time and attributes and children of these components will likely fail in unpredictable ways. Please only render a single instance of <body> and if you need to mount a new one, ensure any previous ones have unmounted first.\n' +
-            '    in body (at **)',
-        ],
-      );
-    } else {
-      expectWarnings(
-        ['svg', 'foreignObject', 'body', 'p'],
-        [
-          'validateDOMNesting(...): <body> cannot appear as a child of <foreignObject>.\n' +
-            '    in body (at **)\n' +
-            '    in foreignObject (at **)',
-        ],
-      );
-    }
+    expectWarnings(
+      ['body', 'body'],
+      [
+        'validateDOMNesting(...): <body> cannot appear as a child of <body>.\n' +
+          '    in body (at **)',
+      ],
+    );
+    expectWarnings(
+      ['svg', 'foreignObject', 'body', 'p'],
+      [
+        'validateDOMNesting(...): <body> cannot appear as a child of <foreignObject>.\n' +
+          '    in body (at **)\n' +
+          '    in foreignObject (at **)',
+        'Warning: You are mounting a new body component when a previous one has not first unmounted. It is an error to render more than one body component at a time and attributes and children of these components will likely fail in unpredictable ways. Please only render a single instance of <body> and if you need to mount a new one, ensure any previous ones have unmounted first.\n' +
+          '    in body (at **)',
+      ],
+    );
   });
 });
diff --git a/packages/react-dom/src/client/ReactDOMLegacy.js b/packages/react-dom/src/client/ReactDOMLegacy.js
index ce0c9ff609ebd..4937ce3f96c0a 100644
--- a/packages/react-dom/src/client/ReactDOMLegacy.js
+++ b/packages/react-dom/src/client/ReactDOMLegacy.js
@@ -43,7 +43,6 @@ import {LegacyRoot} from 'react-reconciler/src/ReactRootTags';
 import getComponentNameFromType from 'shared/getComponentNameFromType';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {has as hasInstance} from 'shared/ReactInstanceMap';
-import {enableHostSingletons} from '../../../shared/ReactFeatureFlags';
 
 const ReactCurrentOwner = ReactSharedInternals.ReactCurrentOwner;
 
@@ -79,21 +78,6 @@ if (__DEV__) {
           'and render the new components instead of calling ReactDOM.render.',
       );
     }
-
-    if (
-      !enableHostSingletons &&
-      container.nodeType === ELEMENT_NODE &&
-      ((container: any): Element).tagName &&
-      ((container: any): Element).tagName.toUpperCase() === 'BODY'
-    ) {
-      console.error(
-        'render(): Rendering components directly into document.body is ' +
-          'discouraged, since its children are often manipulated by third-party ' +
-          'scripts and browser extensions. This may lead to subtle ' +
-          'reconciliation issues. Try rendering into a container element created ' +
-          'for your app.',
-      );
-    }
   };
 }
 
diff --git a/packages/react-dom/src/client/ReactDOMRoot.js b/packages/react-dom/src/client/ReactDOMRoot.js
index ea36929cac5e5..0e3579eb379ae 100644
--- a/packages/react-dom/src/client/ReactDOMRoot.js
+++ b/packages/react-dom/src/client/ReactDOMRoot.js
@@ -18,7 +18,6 @@ import {queueExplicitHydrationTarget} from 'react-dom-bindings/src/events/ReactD
 import {REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
 import {
   enableFloat,
-  enableHostSingletons,
   allowConcurrentByDefault,
   disableCommentsAsDOMContainers,
   enableAsyncActions,
@@ -78,7 +77,6 @@ import {
   createContainer,
   createHydrationContainer,
   updateContainer,
-  findHostInstanceWithNoPortals,
   flushSync,
   isAlreadyRendering,
 } from 'react-reconciler/src/ReactFiberReconciler';
@@ -127,26 +125,6 @@ ReactDOMHydrationRoot.prototype.render = ReactDOMRoot.prototype.render =
             'one argument.',
         );
       }
-
-      const container = root.containerInfo;
-
-      if (
-        !enableFloat &&
-        !enableHostSingletons &&
-        container.nodeType !== COMMENT_NODE
-      ) {
-        const hostInstance = findHostInstanceWithNoPortals(root.current);
-        if (hostInstance) {
-          if (hostInstance.parentNode !== container) {
-            console.error(
-              'render(...): It looks like the React-rendered content of the ' +
-                'root container was removed without using React. This is not ' +
-                'supported and will cause errors. Instead, call ' +
-                "root.unmount() to empty a root's container.",
-            );
-          }
-        }
-      }
     }
     updateContainer(children, root, null, null);
   };
@@ -381,20 +359,6 @@ export function isValidContainerLegacy(node: any): boolean {
 
 function warnIfReactDOMContainerInDEV(container: any) {
   if (__DEV__) {
-    if (
-      !enableHostSingletons &&
-      container.nodeType === ELEMENT_NODE &&
-      ((container: any): Element).tagName &&
-      ((container: any): Element).tagName.toUpperCase() === 'BODY'
-    ) {
-      console.error(
-        'createRoot(): Creating roots directly with document.body is ' +
-          'discouraged, since its children are often manipulated by third-party ' +
-          'scripts and browser extensions. This may lead to subtle ' +
-          'reconciliation issues. Try using a container element created ' +
-          'for your app.',
-      );
-    }
     if (isContainerMarkedAsRoot(container)) {
       if (container._reactRootContainer) {
         console.error(
diff --git a/packages/react-dom/src/test-utils/ReactTestUtils.js b/packages/react-dom/src/test-utils/ReactTestUtils.js
index 04a69bcd81a69..568e8327198f1 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtils.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtils.js
@@ -25,7 +25,7 @@ import {
   rethrowCaughtError,
   invokeGuardedCallbackAndCatchFirstError,
 } from 'shared/ReactErrorUtils';
-import {enableFloat, enableHostSingletons} from 'shared/ReactFeatureFlags';
+import {enableFloat} from 'shared/ReactFeatureFlags';
 import assign from 'shared/assign';
 import isArray from 'shared/isArray';
 
@@ -66,7 +66,7 @@ function findAllInRenderedFiberTreeInternal(fiber, test) {
       node.tag === ClassComponent ||
       node.tag === FunctionComponent ||
       (enableFloat ? node.tag === HostHoistable : false) ||
-      (enableHostSingletons ? node.tag === HostSingleton : false)
+      node.tag === HostSingleton
     ) {
       const publicInst = node.stateNode;
       if (test(publicInst)) {
@@ -419,11 +419,7 @@ function getParent(inst) {
     // events to their parent. We could also go through parentNode on the
     // host node but that wouldn't work for React Native and doesn't let us
     // do the portal feature.
-  } while (
-    inst &&
-    inst.tag !== HostComponent &&
-    (!enableHostSingletons ? true : inst.tag !== HostSingleton)
-  );
+  } while (inst && inst.tag !== HostComponent && inst.tag !== HostSingleton);
   if (inst) {
     return inst;
   }
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index de626f2b72f63..53d7bc601aa05 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -38,7 +38,6 @@ import {
   enableTransitionTracing,
   enableDebugTracing,
   enableFloat,
-  enableHostSingletons,
   enableDO_NOT_USE_disableStrictPassiveEffect,
 } from 'shared/ReactFeatureFlags';
 import {NoFlags, Placement, StaticMask} from './ReactFiberFlags';
@@ -510,12 +509,7 @@ export function createFiberFromTypeAndProps(
       }
     }
   } else if (typeof type === 'string') {
-    if (
-      enableFloat &&
-      supportsResources &&
-      enableHostSingletons &&
-      supportsSingletons
-    ) {
+    if (enableFloat && supportsResources && supportsSingletons) {
       const hostContext = getHostContext();
       fiberTag = isHostHoistableType(type, pendingProps, hostContext)
         ? HostHoistable
@@ -527,7 +521,7 @@ export function createFiberFromTypeAndProps(
       fiberTag = isHostHoistableType(type, pendingProps, hostContext)
         ? HostHoistable
         : HostComponent;
-    } else if (enableHostSingletons && supportsSingletons) {
+    } else if (supportsSingletons) {
       fiberTag = isHostSingletonType(type) ? HostSingleton : HostComponent;
     } else {
       fiberTag = HostComponent;
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 180187a8775ff..dc77d68a38835 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -106,7 +106,6 @@ import {
   enableLegacyHidden,
   enableCPUSuspense,
   enableFloat,
-  enableHostSingletons,
   enableFormActions,
   enableAsyncActions,
   enablePostpone,
@@ -4152,7 +4151,7 @@ function beginWork(
       }
     // Fall through
     case HostSingleton:
-      if (enableHostSingletons && supportsSingletons) {
+      if (supportsSingletons) {
         return updateHostSingleton(current, workInProgress, renderLanes);
       }
     // Fall through
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.js b/packages/react-reconciler/src/ReactFiberCommitWork.js
index 79cd32c4e42a9..13cece7ed9368 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.js
@@ -53,7 +53,6 @@ import {
   enableUseEffectEventHook,
   enableFloat,
   enableLegacyHidden,
-  enableHostSingletons,
   alwaysThrottleRetries,
 } from 'shared/ReactFeatureFlags';
 import {
@@ -1527,9 +1526,7 @@ function hideOrUnhideAllChildren(finishedWork: Fiber, isHidden: boolean) {
         (enableFloat && supportsResources
           ? node.tag === HostHoistable
           : false) ||
-        (enableHostSingletons && supportsSingletons
-          ? node.tag === HostSingleton
-          : false)
+        (supportsSingletons ? node.tag === HostSingleton : false)
       ) {
         if (hostSubtreeRoot === null) {
           hostSubtreeRoot = node;
@@ -1748,9 +1745,7 @@ function isHostParent(fiber: Fiber): boolean {
     fiber.tag === HostComponent ||
     fiber.tag === HostRoot ||
     (enableFloat && supportsResources ? fiber.tag === HostHoistable : false) ||
-    (enableHostSingletons && supportsSingletons
-      ? fiber.tag === HostSingleton
-      : false) ||
+    (supportsSingletons ? fiber.tag === HostSingleton : false) ||
     fiber.tag === HostPortal
   );
 }
@@ -1777,9 +1772,7 @@ function getHostSibling(fiber: Fiber): ?Instance {
     while (
       node.tag !== HostComponent &&
       node.tag !== HostText &&
-      (!(enableHostSingletons && supportsSingletons)
-        ? true
-        : node.tag !== HostSingleton) &&
+      (!supportsSingletons ? true : node.tag !== HostSingleton) &&
       node.tag !== DehydratedFragment
     ) {
       // If it is not host node and, we might have a host node inside it.
@@ -1810,7 +1803,7 @@ function commitPlacement(finishedWork: Fiber): void {
     return;
   }
 
-  if (enableHostSingletons && supportsSingletons) {
+  if (supportsSingletons) {
     if (finishedWork.tag === HostSingleton) {
       // Singletons are already in the Host and don't need to be placed
       // Since they operate somewhat like Portals though their children will
@@ -1823,7 +1816,7 @@ function commitPlacement(finishedWork: Fiber): void {
 
   switch (parentFiber.tag) {
     case HostSingleton: {
-      if (enableHostSingletons && supportsSingletons) {
+      if (supportsSingletons) {
         const parent: Instance = parentFiber.stateNode;
         const before = getHostSibling(finishedWork);
         // We only have the top Fiber that was inserted but we need to recurse down its
@@ -1879,7 +1872,7 @@ function insertOrAppendPlacementNodeIntoContainer(
     }
   } else if (
     tag === HostPortal ||
-    (enableHostSingletons && supportsSingletons ? tag === HostSingleton : false)
+    (supportsSingletons ? tag === HostSingleton : false)
   ) {
     // If the insertion itself is a portal, then we don't want to traverse
     // down its children. Instead, we'll get insertions from each child in
@@ -1914,7 +1907,7 @@ function insertOrAppendPlacementNode(
     }
   } else if (
     tag === HostPortal ||
-    (enableHostSingletons && supportsSingletons ? tag === HostSingleton : false)
+    (supportsSingletons ? tag === HostSingleton : false)
   ) {
     // If the insertion itself is a portal, then we don't want to traverse
     // down its children. Instead, we'll get insertions from each child in
@@ -2048,7 +2041,7 @@ function commitDeletionEffectsOnFiber(
       // Fall through
     }
     case HostSingleton: {
-      if (enableHostSingletons && supportsSingletons) {
+      if (supportsSingletons) {
         if (!offscreenSubtreeWasHidden) {
           safelyDetachRef(deletedFiber, nearestMountedAncestor);
         }
@@ -2711,7 +2704,7 @@ function commitMutationEffectsOnFiber(
       // Fall through
     }
     case HostSingleton: {
-      if (enableHostSingletons && supportsSingletons) {
+      if (supportsSingletons) {
         if (flags & Update) {
           const previousWork = finishedWork.alternate;
           if (previousWork === null) {
diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.js b/packages/react-reconciler/src/ReactFiberCompleteWork.js
index 411dee4c0b0bf..78dd30cd5f325 100644
--- a/packages/react-reconciler/src/ReactFiberCompleteWork.js
+++ b/packages/react-reconciler/src/ReactFiberCompleteWork.js
@@ -33,7 +33,6 @@ import type {TracingMarkerInstance} from './ReactFiberTracingMarkerComponent';
 import type {Cache} from './ReactFiberCacheComponent';
 import {
   enableLegacyHidden,
-  enableHostSingletons,
   enableSuspenseCallback,
   enableScopeAPI,
   enableProfilerTimer,
@@ -233,9 +232,7 @@ function appendAllChildren(
         appendInitialChild(parent, node.stateNode);
       } else if (
         node.tag === HostPortal ||
-        (enableHostSingletons && supportsSingletons
-          ? node.tag === HostSingleton
-          : false)
+        (supportsSingletons ? node.tag === HostSingleton : false)
       ) {
         // If we have a portal child, then we don't want to traverse
         // down its children. Instead, we'll get insertions from each child in
@@ -1177,7 +1174,7 @@ function completeWork(
       // Fall through
     }
     case HostSingleton: {
-      if (enableHostSingletons && supportsSingletons) {
+      if (supportsSingletons) {
         popHostContext(workInProgress);
         const rootContainerInstance = getRootHostContainer();
         const type = workInProgress.type;
diff --git a/packages/react-reconciler/src/ReactFiberHotReloading.js b/packages/react-reconciler/src/ReactFiberHotReloading.js
index 3bc3755bb957a..090f1311b4453 100644
--- a/packages/react-reconciler/src/ReactFiberHotReloading.js
+++ b/packages/react-reconciler/src/ReactFiberHotReloading.js
@@ -14,7 +14,7 @@ import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Instance} from './ReactFiberConfig';
 import type {ReactNodeList} from 'shared/ReactTypes';
 
-import {enableHostSingletons, enableFloat} from 'shared/ReactFeatureFlags';
+import {enableFloat} from 'shared/ReactFeatureFlags';
 import {
   flushSync,
   scheduleUpdateOnFiber,
@@ -469,9 +469,7 @@ function findChildHostInstancesForFiberShallowly(
       if (
         node.tag === HostComponent ||
         (enableFloat ? node.tag === HostHoistable : false) ||
-        (enableHostSingletons && supportsSingletons
-          ? node.tag === HostSingleton
-          : false)
+        (supportsSingletons ? node.tag === HostSingleton : false)
       ) {
         // We got a match.
         foundHostInstances = true;
diff --git a/packages/react-reconciler/src/ReactFiberHydrationContext.js b/packages/react-reconciler/src/ReactFiberHydrationContext.js
index c1ee83c2c8e71..a0838ea331b3c 100644
--- a/packages/react-reconciler/src/ReactFiberHydrationContext.js
+++ b/packages/react-reconciler/src/ReactFiberHydrationContext.js
@@ -35,10 +35,7 @@ import {
   NoFlags,
   DidCapture,
 } from './ReactFiberFlags';
-import {
-  enableHostSingletons,
-  enableClientRenderFallbackOnTextMismatch,
-} from 'shared/ReactFeatureFlags';
+import {enableClientRenderFallbackOnTextMismatch} from 'shared/ReactFeatureFlags';
 
 import {
   createFiberFromHostInstanceForDeletion,
@@ -426,7 +423,7 @@ function throwOnHydrationMismatch(fiber: Fiber) {
 }
 
 function claimHydratableSingleton(fiber: Fiber): void {
-  if (enableHostSingletons && supportsSingletons) {
+  if (supportsSingletons) {
     if (!isHydrating) {
       return;
     }
@@ -801,7 +798,7 @@ function popHydrationState(fiber: Fiber): boolean {
   }
 
   let shouldClear = false;
-  if (enableHostSingletons && supportsSingletons) {
+  if (supportsSingletons) {
     // With float we never clear the Root, or Singleton instances. We also do not clear Instances
     // that have singleton text content
     if (
diff --git a/packages/react-reconciler/src/ReactFiberTreeReflection.js b/packages/react-reconciler/src/ReactFiberTreeReflection.js
index 8828017eee8d3..c5c5944efda6b 100644
--- a/packages/react-reconciler/src/ReactFiberTreeReflection.js
+++ b/packages/react-reconciler/src/ReactFiberTreeReflection.js
@@ -25,7 +25,7 @@ import {
   SuspenseComponent,
 } from './ReactWorkTags';
 import {NoFlags, Placement, Hydrating} from './ReactFiberFlags';
-import {enableFloat, enableHostSingletons} from 'shared/ReactFeatureFlags';
+import {enableFloat} from 'shared/ReactFeatureFlags';
 
 const ReactCurrentOwner = ReactSharedInternals.ReactCurrentOwner;
 
@@ -281,7 +281,7 @@ function findCurrentHostFiberImpl(node: Fiber): Fiber | null {
   if (
     tag === HostComponent ||
     (enableFloat ? tag === HostHoistable : false) ||
-    (enableHostSingletons ? tag === HostSingleton : false) ||
+    tag === HostSingleton ||
     tag === HostText
   ) {
     return node;
@@ -312,7 +312,7 @@ function findCurrentHostFiberWithNoPortalsImpl(node: Fiber): Fiber | null {
   if (
     tag === HostComponent ||
     (enableFloat ? tag === HostHoistable : false) ||
-    (enableHostSingletons ? tag === HostSingleton : false) ||
+    tag === HostSingleton ||
     tag === HostText
   ) {
     return node;
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index 7411bc7d9a92c..2ede92b1c06e0 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -105,8 +105,6 @@ export const enableSuspenseAvoidThisFallbackFizz = false;
 
 export const enableCPUSuspense = __EXPERIMENTAL__;
 
-export const enableHostSingletons = true;
-
 export const enableFloat = true;
 
 // Enables unstable_useMemoCache hook, intended as a compilation target for
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index 0c04991e13b7d..5c224fd78271f 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -83,7 +83,6 @@ export const enableServerContext = false;
 export const enableTransitionTracing = false;
 
 export const enableFloat = true;
-export const enableHostSingletons = true;
 
 export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index 70105f99ce48e..b8203b3b3cbcb 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -68,7 +68,6 @@ export const enableServerContext = false;
 export const enableTransitionTracing = false;
 
 export const enableFloat = true;
-export const enableHostSingletons = true;
 
 export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index 1f1766c61789a..611160e2a1f6a 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -68,7 +68,6 @@ export const enableServerContext = false;
 export const enableTransitionTracing = false;
 
 export const enableFloat = true;
-export const enableHostSingletons = true;
 
 export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
index 18fa67530ad5d..60a15318c7c00 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.native.js
@@ -66,7 +66,6 @@ export const enableServerContext = false;
 export const enableTransitionTracing = false;
 
 export const enableFloat = true;
-export const enableHostSingletons = true;
 
 export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index c4131e3312c54..c5678792313ae 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -68,7 +68,6 @@ export const enableServerContext = false;
 export const enableTransitionTracing = false;
 
 export const enableFloat = true;
-export const enableHostSingletons = true;
 
 export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index a597b8e98058c..01ae3eae5935c 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -54,7 +54,6 @@ export const enableCPUSuspense = true;
 export const enableFloat = true;
 export const enableUseMemoCacheHook = true;
 export const enableUseEffectEventHook = true;
-export const enableHostSingletons = true;
 export const enableClientRenderFallbackOnTextMismatch = false;
 export const enableFilterEmptyStringAttributesDOM = true;