diff --git a/packages/react/src/__tests__/ReactJSXRuntime-test.js b/packages/react/src/__tests__/ReactJSXRuntime-test.js
index d25079258327..0ed8391f3605 100644
--- a/packages/react/src/__tests__/ReactJSXRuntime-test.js
+++ b/packages/react/src/__tests__/ReactJSXRuntime-test.js
@@ -374,4 +374,37 @@ describe('ReactJSXRuntime', () => {
     }
     expect(didCall).toBe(false);
   });
+
+  // @gate enableRefAsProp
+  // @gate disableStringRefs
+  it('does not clone props object if key is not spread', async () => {
+    const config = {
+      foo: 'foo',
+      bar: 'bar',
+    };
+
+    const element = __DEV__
+      ? JSXDEVRuntime.jsxDEV('div', config)
+      : JSXRuntime.jsx('div', config);
+    expect(element.props).toBe(config);
+
+    const configWithKey = {
+      foo: 'foo',
+      bar: 'bar',
+      // This only happens when the key is spread onto the element. A statically
+      // defined key is passed as a separate argument to the jsx() runtime.
+      key: 'key',
+    };
+
+    let elementWithSpreadKey;
+    expect(() => {
+      elementWithSpreadKey = __DEV__
+        ? JSXDEVRuntime.jsxDEV('div', configWithKey)
+        : JSXRuntime.jsx('div', configWithKey);
+    }).toErrorDev(
+      'A props object containing a "key" prop is being spread into JSX',
+      {withoutStack: true},
+    );
+    expect(elementWithSpreadKey.props).not.toBe(configWithKey);
+  });
 });
diff --git a/packages/react/src/jsx/ReactJSXElement.js b/packages/react/src/jsx/ReactJSXElement.js
index d52355b18468..03e46d6d952b 100644
--- a/packages/react/src/jsx/ReactJSXElement.js
+++ b/packages/react/src/jsx/ReactJSXElement.js
@@ -314,11 +314,6 @@ function ReactElement(type, key, _ref, self, source, owner, props) {
  * @param {string} key
  */
 export function jsxProd(type, config, maybeKey) {
-  let propName;
-
-  // Reserved names are extracted
-  const props = {};
-
   let key = null;
   let ref = null;
 
@@ -351,22 +346,39 @@ export function jsxProd(type, config, maybeKey) {
     }
   }
 
-  // Remaining properties are added to a new props object
-  for (propName in config) {
-    if (
-      hasOwnProperty.call(config, propName) &&
-      // Skip over reserved prop names
-      propName !== 'key' &&
-      (enableRefAsProp || propName !== 'ref')
-    ) {
-      if (enableRefAsProp && !disableStringRefs && propName === 'ref') {
-        props.ref = coerceStringRef(
-          config[propName],
-          ReactCurrentOwner.current,
-          type,
-        );
-      } else {
-        props[propName] = config[propName];
+  let props;
+  if (enableRefAsProp && disableStringRefs && !('key' in config)) {
+    // If key was not spread in, we can reuse the original props object. This
+    // only works for `jsx`, not `createElement`, because `jsx` is a compiler
+    // target and the compiler always passes a new object. For `createElement`,
+    // we can't assume a new object is passed every time because it can be
+    // called manually.
+    //
+    // Spreading key is a warning in dev. In a future release, we will not
+    // remove a spread key from the props object. (But we'll still warn.) We'll
+    // always pass the object straight through.
+    props = config;
+  } else {
+    // We need to remove reserved props (key, prop, ref). Create a fresh props
+    // object and copy over all the non-reserved props. We don't use `delete`
+    // because in V8 it will deopt the object to dictionary mode.
+    props = {};
+    for (const propName in config) {
+      if (
+        hasOwnProperty.call(config, propName) &&
+        // Skip over reserved prop names
+        propName !== 'key' &&
+        (enableRefAsProp || propName !== 'ref')
+      ) {
+        if (enableRefAsProp && !disableStringRefs && propName === 'ref') {
+          props.ref = coerceStringRef(
+            config[propName],
+            ReactCurrentOwner.current,
+            type,
+          );
+        } else {
+          props[propName] = config[propName];
+        }
       }
     }
   }
@@ -375,7 +387,7 @@ export function jsxProd(type, config, maybeKey) {
     // Resolve default props
     if (type && type.defaultProps) {
       const defaultProps = type.defaultProps;
-      for (propName in defaultProps) {
+      for (const propName in defaultProps) {
         if (props[propName] === undefined) {
           props[propName] = defaultProps[propName];
         }
@@ -538,11 +550,6 @@ export function jsxDEV(type, config, maybeKey, isStaticChildren, source, self) {
       }
     }
 
-    let propName;
-
-    // Reserved names are extracted
-    const props = {};
-
     let key = null;
     let ref = null;
 
@@ -578,22 +585,39 @@ export function jsxDEV(type, config, maybeKey, isStaticChildren, source, self) {
       }
     }
 
-    // Remaining properties are added to a new props object
-    for (propName in config) {
-      if (
-        hasOwnProperty.call(config, propName) &&
-        // Skip over reserved prop names
-        propName !== 'key' &&
-        (enableRefAsProp || propName !== 'ref')
-      ) {
-        if (enableRefAsProp && !disableStringRefs && propName === 'ref') {
-          props.ref = coerceStringRef(
-            config[propName],
-            ReactCurrentOwner.current,
-            type,
-          );
-        } else {
-          props[propName] = config[propName];
+    let props;
+    if (enableRefAsProp && disableStringRefs && !('key' in config)) {
+      // If key was not spread in, we can reuse the original props object. This
+      // only works for `jsx`, not `createElement`, because `jsx` is a compiler
+      // target and the compiler always passes a new object. For `createElement`,
+      // we can't assume a new object is passed every time because it can be
+      // called manually.
+      //
+      // Spreading key is a warning in dev. In a future release, we will not
+      // remove a spread key from the props object. (But we'll still warn.) We'll
+      // always pass the object straight through.
+      props = config;
+    } else {
+      // We need to remove reserved props (key, prop, ref). Create a fresh props
+      // object and copy over all the non-reserved props. We don't use `delete`
+      // because in V8 it will deopt the object to dictionary mode.
+      props = {};
+      for (const propName in config) {
+        if (
+          hasOwnProperty.call(config, propName) &&
+          // Skip over reserved prop names
+          propName !== 'key' &&
+          (enableRefAsProp || propName !== 'ref')
+        ) {
+          if (enableRefAsProp && !disableStringRefs && propName === 'ref') {
+            props.ref = coerceStringRef(
+              config[propName],
+              ReactCurrentOwner.current,
+              type,
+            );
+          } else {
+            props[propName] = config[propName];
+          }
         }
       }
     }
@@ -602,7 +626,7 @@ export function jsxDEV(type, config, maybeKey, isStaticChildren, source, self) {
       // Resolve default props
       if (type && type.defaultProps) {
         const defaultProps = type.defaultProps;
-        for (propName in defaultProps) {
+        for (const propName in defaultProps) {
           if (props[propName] === undefined) {
             props[propName] = defaultProps[propName];
           }