diff --git a/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Legacy-itest.js b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Legacy-itest.js
new file mode 100644
index 00000000000..6c1477aa7b5
--- /dev/null
+++ b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Legacy-itest.js
@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import setUpReactFabricPublicInstanceFantomTests from './setUpReactFabricPublicInstanceFantomTests';
+
+setUpReactFabricPublicInstanceFantomTests({isModern: false});
diff --git a/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Modern-itest.js b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Modern-itest.js
new file mode 100644
index 00000000000..9f66d43eacc
--- /dev/null
+++ b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/ReactFabricPublicInstance-Modern-itest.js
@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import './setUpFeatureFlags';
+import setUpReactFabricPublicInstanceFantomTests from './setUpReactFabricPublicInstanceFantomTests';
+
+setUpReactFabricPublicInstanceFantomTests({isModern: true});
diff --git a/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpFeatureFlags.js b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpFeatureFlags.js
new file mode 100644
index 00000000000..a5a75c44ac4
--- /dev/null
+++ b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpFeatureFlags.js
@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import * as ReactNativeFeatureFlags from '../../../../src/private/featureflags/ReactNativeFeatureFlags';
+
+ReactNativeFeatureFlags.override({
+  enableAccessToHostTreeInFabric: () => true,
+});
diff --git a/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpReactFabricPublicInstanceFantomTests.js b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpReactFabricPublicInstanceFantomTests.js
new file mode 100644
index 00000000000..c62b508a2a8
--- /dev/null
+++ b/packages/react-native/Libraries/ReactNative/ReactFabricPublicInstance/__tests__/setUpReactFabricPublicInstanceFantomTests.js
@@ -0,0 +1,365 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import '../../../Core/InitializeCore.js';
+
+import * as ReactNativeTester from '../../../../src/private/__tests__/ReactNativeTester';
+import ReactNativeElement from '../../../../src/private/webapis/dom/nodes/ReactNativeElement';
+import TextInputState from '../../../Components/TextInput/TextInputState';
+import View from '../../../Components/View/View';
+import ReactFabricHostComponent from '../ReactFabricHostComponent';
+import nullthrows from 'nullthrows';
+import * as React from 'react';
+
+export default function setUpTests({isModern}: {isModern: boolean}) {
+  // TODO: move these tests to the test file for `ReactNativeElement` when the legacy implementation is removed.
+  describe(`ReactFabricPublicInstance (${isModern ? 'modern' : 'legacy'})`, () => {
+    it('should provide instances of the right class as refs in host components', () => {
+      let node;
+
+      const root = ReactNativeTester.createRoot();
+      ReactNativeTester.runTask(() => {
+        root.render(
+          <View
+            ref={receivedNode => {
+              node = receivedNode;
+            }}
+          />,
+        );
+      });
+
+      expect(node).toBeInstanceOf(
+        isModern ? ReactNativeElement : ReactFabricHostComponent,
+      );
+    });
+
+    describe('blur', () => {
+      test('blur() invokes TextInputState', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        const blurTextInput = jest.fn();
+
+        // We don't support view commands in Fantom yet, so we have to mock this.
+        TextInputState.blurTextInput = blurTextInput;
+
+        ReactNativeTester.runTask(() => {
+          node.blur();
+        });
+
+        expect(blurTextInput).toHaveBeenCalledTimes(1);
+        expect(blurTextInput.mock.calls).toEqual([[node]]);
+      });
+    });
+
+    describe('focus', () => {
+      test('focus() invokes TextInputState', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        const focusTextInput = jest.fn();
+
+        // We don't support view commands in Fantom yet, so we have to mock this.
+        TextInputState.focusTextInput = focusTextInput;
+
+        ReactNativeTester.runTask(() => {
+          node.focus();
+        });
+
+        expect(focusTextInput).toHaveBeenCalledTimes(1);
+        expect(focusTextInput.mock.calls).toEqual([[node]]);
+      });
+    });
+
+    describe('measure', () => {
+      it('component.measure(...) invokes callback', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        const callback = jest.fn();
+        node.measure(callback);
+
+        expect(callback).toHaveBeenCalledTimes(1);
+        expect(callback.mock.calls).toEqual([[10, 10, 100, 100, 10, 10]]);
+      });
+
+      it('unmounted.measure(...) does nothing', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        ReactNativeTester.runTask(() => {
+          root.render(<></>);
+        });
+
+        const callback = jest.fn();
+        node.measure(callback);
+
+        expect(callback).not.toHaveBeenCalled();
+      });
+    });
+
+    describe('measureInWindow', () => {
+      it('component.measureInWindow(...) invokes callback', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        const callback = jest.fn();
+        node.measureInWindow(callback);
+
+        expect(callback).toHaveBeenCalledTimes(1);
+        expect(callback.mock.calls).toEqual([[10, 10, 100, 100]]);
+      });
+
+      it('unmounted.measureInWindow(...) does nothing', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeNode = node;
+              }}
+            />,
+          );
+        });
+
+        const node = nullthrows(maybeNode);
+
+        ReactNativeTester.runTask(() => {
+          root.render(<></>);
+        });
+
+        const callback = jest.fn();
+        node.measureInWindow(callback);
+
+        expect(callback).not.toHaveBeenCalled();
+      });
+    });
+
+    describe('measureLayout', () => {
+      it('component.measureLayout(component, ...) invokes callback', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeParentNode;
+        let maybeChildNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeParentNode = node;
+              }}>
+              <View
+                style={{width: 10, height: 10, left: 20, top: 20}}
+                ref={node => {
+                  maybeChildNode = node;
+                }}
+              />
+            </View>,
+          );
+        });
+
+        const parentNode = nullthrows(maybeParentNode);
+        const childNode = nullthrows(maybeChildNode);
+
+        const callback = jest.fn();
+        childNode.measureLayout(parentNode, callback);
+
+        expect(callback).toHaveBeenCalledTimes(1);
+        expect(callback.mock.calls).toEqual([[20, 20, 10, 10]]);
+      });
+
+      it('unmounted.measureLayout(component, ...) does nothing', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeParentNode;
+        let maybeChildNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeParentNode = node;
+              }}>
+              <View
+                style={{width: 10, height: 10, left: 20, top: 20}}
+                ref={node => {
+                  maybeChildNode = node;
+                }}
+              />
+            </View>,
+          );
+        });
+
+        const parentNode = nullthrows(maybeParentNode);
+        const childNode = nullthrows(maybeChildNode);
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View style={{width: 100, height: 100, left: 10, top: 10}} />,
+          );
+        });
+
+        const callback = jest.fn();
+        childNode.measureLayout(parentNode, callback);
+
+        expect(callback).not.toHaveBeenCalled();
+      });
+
+      it('component.measureLayout(unmounted, ...) does nothing', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeParentNode;
+        let maybeChildNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeParentNode = node;
+              }}>
+              <View
+                style={{width: 10, height: 10, left: 20, top: 20}}
+                ref={node => {
+                  maybeChildNode = node;
+                }}
+              />
+            </View>,
+          );
+        });
+
+        const parentNode = nullthrows(maybeParentNode);
+        const childNode = nullthrows(maybeChildNode);
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View style={{width: 100, height: 100, left: 10, top: 10}} />,
+          );
+        });
+
+        const callback = jest.fn();
+        parentNode.measureLayout(childNode, callback);
+
+        expect(callback).not.toHaveBeenCalled();
+      });
+
+      it('unmounted.measureLayout(unmounted, ...) does nothing', () => {
+        const root = ReactNativeTester.createRoot();
+
+        let maybeParentNode;
+        let maybeChildNode;
+
+        ReactNativeTester.runTask(() => {
+          root.render(
+            <View
+              style={{width: 100, height: 100, left: 10, top: 10}}
+              ref={node => {
+                maybeParentNode = node;
+              }}>
+              <View
+                style={{width: 10, height: 10, left: 20, top: 20}}
+                ref={node => {
+                  maybeChildNode = node;
+                }}
+              />
+            </View>,
+          );
+        });
+
+        const parentNode = nullthrows(maybeParentNode);
+        const childNode = nullthrows(maybeChildNode);
+
+        ReactNativeTester.runTask(() => {
+          root.render(<></>);
+        });
+
+        const callback = jest.fn();
+        childNode.measureLayout(parentNode, callback);
+
+        expect(callback).not.toHaveBeenCalled();
+      });
+    });
+  });
+}