diff --git a/packages/babel-plugin-proposal-private-property-in-object/package.json b/packages/babel-plugin-proposal-private-property-in-object/package.json
index 385e50f0436d..c66badfdb787 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/package.json
+++ b/packages/babel-plugin-proposal-private-property-in-object/package.json
@@ -18,7 +18,8 @@
   ],
   "dependencies": {
     "@babel/helper-create-class-features-plugin": "workspace:^7.13.0",
-    "@babel/helper-plugin-utils": "workspace:^7.13.0"
+    "@babel/helper-plugin-utils": "workspace:^7.13.0",
+    "@babel/plugin-syntax-private-property-in-object": "workspace:^7.13.0"
   },
   "peerDependencies": {
     "@babel/core": "^7.0.0-0"
diff --git a/packages/babel-plugin-proposal-private-property-in-object/src/index.js b/packages/babel-plugin-proposal-private-property-in-object/src/index.js
index c8c5c7bddcc0..f0c1ad5e43f9 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/src/index.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/src/index.js
@@ -6,15 +6,21 @@ import {
   FEATURES,
 } from "@babel/helper-create-class-features-plugin";
 
+import pluginPrivateIn from "./native-private-fields";
+
 export default declare((api, options) => {
   api.assertVersion(7);
 
+  const { loose, nativePrivateFields } = options;
+
+  if (nativePrivateFields) return pluginPrivateIn(api);
+
   return createClassFeaturePlugin({
     name: "proposal-class-properties",
 
     api,
     feature: FEATURES.privateIn,
-    loose: options.loose,
+    loose,
 
     manipulateOptions(opts, parserOpts) {
       parserOpts.plugins.push("privateIn");
diff --git a/packages/babel-plugin-proposal-private-property-in-object/src/native-private-fields.js b/packages/babel-plugin-proposal-private-property-in-object/src/native-private-fields.js
new file mode 100644
index 000000000000..686eab8cdc7c
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/src/native-private-fields.js
@@ -0,0 +1,67 @@
+import syntaxPlugin from "@babel/plugin-syntax-private-property-in-object";
+import { injectInitialization } from "@babel/helper-create-class-features-plugin";
+
+export default function pluginPrivateIn({ types: t, template }) {
+  const ids = new WeakMap();
+
+  return {
+    name: "proposal-private-property-in-object",
+    inherits: syntaxPlugin,
+    visitor: {
+      BinaryExpression(path) {
+        const { node } = path;
+        if (node.operator !== "in") return;
+        if (!t.isPrivateName(node.left)) return;
+
+        const { name } = node.left.id;
+
+        let isStatic;
+        const outerClass = path.findParent(path => {
+          if (!path.isClass()) return false;
+
+          const privateElement = path.node.body.body.find(
+            node => t.isPrivate(node) && node.key.id.name === name,
+          );
+          if (!privateElement) return false;
+
+          isStatic = privateElement.static;
+          return true;
+        });
+
+        if (isStatic) {
+          if (!outerClass.node.id) {
+            outerClass.set("id", path.scope.generateUidIdentifier("class"));
+          }
+          path.replaceWith(
+            template.expression.ast`
+              ${t.cloneNode(outerClass.node.id)} === ${path.node.right}
+            `,
+          );
+          return;
+        }
+
+        let id = ids.get(outerClass.node);
+        if (!id) {
+          id = outerClass.scope.generateUidIdentifier(
+            `${outerClass.node.id?.name || ""} brandCheck`,
+          );
+          ids.set(outerClass.node, id);
+
+          const constructor = outerClass
+            .get("body.body")
+            .find(el => el.isClassMethod({ kind: "constructor" }));
+
+          injectInitialization(outerClass, constructor, [
+            template.ast`${t.cloneNode(id)}.add(this)`,
+          ]);
+
+          outerClass.insertBefore(template.ast`var ${id} = new WeakSet()`);
+        }
+
+        path.replaceWith(
+          template.ast`${t.cloneNode(id)}.has(${path.node.right})`,
+        );
+      },
+    },
+  };
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/input.js
new file mode 100644
index 000000000000..c0e9000615fd
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  get #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/output.js
new file mode 100644
index 000000000000..7a64679f5a1a
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/output.js
@@ -0,0 +1,14 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  get #foo() {}
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/input.js
new file mode 100644
index 000000000000..3d817b01b547
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/input.js
@@ -0,0 +1,9 @@
+function fn() {
+  return new class {
+    #priv;
+
+    method(obj) {
+      return #priv in obj;
+    }
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/output.js
new file mode 100644
index 000000000000..b52693938314
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/output.js
@@ -0,0 +1,16 @@
+function fn() {
+  var _brandCheck;
+
+  return new (_brandCheck = new WeakSet(), class {
+    constructor() {
+      _brandCheck.add(this);
+    }
+
+    #priv;
+
+    method(obj) {
+      return _brandCheck.has(obj);
+    }
+
+  })();
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/input.js
new file mode 100644
index 000000000000..8f394f3d4c76
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/input.js
@@ -0,0 +1,9 @@
+function fn() {
+  return new class {
+    static #priv;
+
+    method(obj) {
+      return #priv in obj;
+    }
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/output.js
new file mode 100644
index 000000000000..20a1dff648cf
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/output.js
@@ -0,0 +1,10 @@
+function fn() {
+  return new class _class {
+    static #priv;
+
+    method(obj) {
+      return _class === obj;
+    }
+
+  }();
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/input.js
new file mode 100644
index 000000000000..a682a1a15c5b
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  #foo = 1;
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/output.js
new file mode 100644
index 000000000000..06c9ccc921e6
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/output.js
@@ -0,0 +1,14 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo = 1;
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/input.js
new file mode 100644
index 000000000000..365843c59708
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/output.js
new file mode 100644
index 000000000000..59a6fb1062f8
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/output.js
@@ -0,0 +1,14 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo() {}
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/input.js
new file mode 100644
index 000000000000..a084dd06afd6
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/input.js
@@ -0,0 +1,18 @@
+class Foo {
+  #foo = 1;
+  #bar = 1;
+
+  test() {
+    class Nested {
+      #bar = 2;
+
+      test() {
+        #foo in this;
+        #bar in this;
+      }
+    }
+
+    #foo in this;
+    #bar in this;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/output.js
new file mode 100644
index 000000000000..881b784ec5b5
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/output.js
@@ -0,0 +1,34 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo = 1;
+  #bar = 1;
+
+  test() {
+    var _NestedBrandCheck = new WeakSet();
+
+    class Nested {
+      constructor() {
+        _NestedBrandCheck.add(this);
+      }
+
+      #bar = 2;
+
+      test() {
+        _FooBrandCheck.has(this);
+
+        _NestedBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+
+    _FooBrandCheck.has(this);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/input.js
new file mode 100644
index 000000000000..2258be35c5fd
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/input.js
@@ -0,0 +1,15 @@
+class Foo {
+  #foo = 1;
+
+  test() {
+    class Nested {
+      #foo = 2;
+
+      test() {
+        #foo in this;
+      }
+    }
+
+    #foo in this;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/output.js
new file mode 100644
index 000000000000..a761903ba09a
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/output.js
@@ -0,0 +1,29 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo = 1;
+
+  test() {
+    var _NestedBrandCheck = new WeakSet();
+
+    class Nested {
+      constructor() {
+        _NestedBrandCheck.add(this);
+      }
+
+      #foo = 2;
+
+      test() {
+        _NestedBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/input.js
new file mode 100644
index 000000000000..e17e438b314d
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/input.js
@@ -0,0 +1,13 @@
+class Foo {
+  #foo = 1;
+
+  test() {
+    class Nested {
+      test() {
+        #foo in this;
+      }
+    }
+
+    #foo in this;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/output.js
new file mode 100644
index 000000000000..ab0ea8eebfef
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/output.js
@@ -0,0 +1,21 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo = 1;
+
+  test() {
+    class Nested {
+      test() {
+        _FooBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/options.json b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/options.json
new file mode 100644
index 000000000000..1727d6dba8e5
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/options.json
@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["proposal-private-property-in-object", { "nativePrivateFields": true }],
+    "syntax-class-properties"
+  ]
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/input.js
new file mode 100644
index 000000000000..e74333f2055f
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  static get #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/output.js
new file mode 100644
index 000000000000..cdec0d002314
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-accessor/output.js
@@ -0,0 +1,8 @@
+class Foo {
+  static get #foo() {}
+
+  test(other) {
+    return Foo === other;
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/input.js
new file mode 100644
index 000000000000..a4f771844fe9
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  static #foo = 1;
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/output.js
new file mode 100644
index 000000000000..823c53b802cf
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-field/output.js
@@ -0,0 +1,8 @@
+class Foo {
+  static #foo = 1;
+
+  test(other) {
+    return Foo === other;
+  }
+
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/input.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/input.js
new file mode 100644
index 000000000000..9fffe7a01622
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/input.js
@@ -0,0 +1,7 @@
+class Foo {
+  static #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/output.js
new file mode 100644
index 000000000000..bb657d68eb23
--- /dev/null
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/static-method/output.js
@@ -0,0 +1,8 @@
+class Foo {
+  static #foo() {}
+
+  test(other) {
+    return Foo === other;
+  }
+
+}
diff --git a/packages/babel-plugin-syntax-private-property-in-object/.npmignore b/packages/babel-plugin-syntax-private-property-in-object/.npmignore
new file mode 100644
index 000000000000..f9806945836e
--- /dev/null
+++ b/packages/babel-plugin-syntax-private-property-in-object/.npmignore
@@ -0,0 +1,3 @@
+src
+test
+*.log
diff --git a/packages/babel-plugin-syntax-private-property-in-object/README.md b/packages/babel-plugin-syntax-private-property-in-object/README.md
new file mode 100644
index 000000000000..8dd2f6b32cb2
--- /dev/null
+++ b/packages/babel-plugin-syntax-private-property-in-object/README.md
@@ -0,0 +1,19 @@
+# @babel/plugin-syntax-class-static-block
+
+> Allow parsing of class static blocks
+
+See our website [@babel/plugin-syntax-class-static-block](https://babeljs.io/docs/en/babel-plugin-syntax-class-static-block) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-syntax-class-static-block
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-syntax-class-static-block --dev
+```
diff --git a/packages/babel-plugin-syntax-private-property-in-object/package.json b/packages/babel-plugin-syntax-private-property-in-object/package.json
new file mode 100644
index 000000000000..544e52ee4bea
--- /dev/null
+++ b/packages/babel-plugin-syntax-private-property-in-object/package.json
@@ -0,0 +1,28 @@
+{
+  "name": "@babel/plugin-syntax-private-property-in-object",
+  "version": "7.13.0",
+  "description": "Allow parsing of '#foo in obj' brand checks",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/babel/babel.git",
+    "directory": "packages/babel-plugin-syntax-private-property-in-object"
+  },
+  "homepage": "https://babel.dev/docs/en/next/babel-plugin-syntax-private-property-in-object",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "main": "./lib/index.js",
+  "exports": {
+    ".": "./lib/index.js"
+  },
+  "keywords": [
+    "babel-plugin"
+  ],
+  "dependencies": {
+    "@babel/helper-plugin-utils": "workspace:^7.12.13"
+  },
+  "peerDependencies": {
+    "@babel/core": "^7.0.0-0"
+  }
+}
diff --git a/packages/babel-plugin-syntax-private-property-in-object/src/index.js b/packages/babel-plugin-syntax-private-property-in-object/src/index.js
new file mode 100644
index 000000000000..a716fe39e301
--- /dev/null
+++ b/packages/babel-plugin-syntax-private-property-in-object/src/index.js
@@ -0,0 +1,13 @@
+import { declare } from "@babel/helper-plugin-utils";
+
+export default declare(api => {
+  api.assertVersion(7);
+
+  return {
+    name: "syntax-private-property-in-object",
+
+    manipulateOptions(opts, parserOpts) {
+      parserOpts.plugins.push("privateIn");
+    },
+  };
+});
diff --git a/yarn.lock b/yarn.lock
index a22617a45714..f611585368d7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1447,6 +1447,7 @@ __metadata:
     "@babel/helper-create-class-features-plugin": "workspace:^7.13.0"
     "@babel/helper-plugin-test-runner": "workspace:*"
     "@babel/helper-plugin-utils": "workspace:^7.13.0"
+    "@babel/plugin-syntax-private-property-in-object": "workspace:^7.13.0"
   peerDependencies:
     "@babel/core": ^7.0.0-0
   languageName: unknown
@@ -1821,6 +1822,16 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@babel/plugin-syntax-private-property-in-object@workspace:^7.13.0, @babel/plugin-syntax-private-property-in-object@workspace:packages/babel-plugin-syntax-private-property-in-object":
+  version: 0.0.0-use.local
+  resolution: "@babel/plugin-syntax-private-property-in-object@workspace:packages/babel-plugin-syntax-private-property-in-object"
+  dependencies:
+    "@babel/helper-plugin-utils": "workspace:^7.12.13"
+  peerDependencies:
+    "@babel/core": ^7.0.0-0
+  languageName: unknown
+  linkType: soft
+
 "@babel/plugin-syntax-record-and-tuple@workspace:*, @babel/plugin-syntax-record-and-tuple@workspace:^7.12.1, @babel/plugin-syntax-record-and-tuple@workspace:packages/babel-plugin-syntax-record-and-tuple":
   version: 0.0.0-use.local
   resolution: "@babel/plugin-syntax-record-and-tuple@workspace:packages/babel-plugin-syntax-record-and-tuple"