diff --git a/.changeset/config.json b/.changeset/config.json
index 27db2bd13ab..8a7e96564c6 100644
--- a/.changeset/config.json
+++ b/.changeset/config.json
@@ -15,7 +15,9 @@
     "firebase-messaging-integration-test",
     "firebase-compat-interop-test",
     "firebase-compat-typings-test",
+    "@firebase/app-compat",
     "@firebase/app-exp",
+    "@firebase/app-check-compat",
     "@firebase/app-check-exp",
     "@firebase/analytics-compat",
     "@firebase/analytics-exp",
@@ -32,7 +34,6 @@
     "@firebase/remote-config-exp",
     "@firebase/remote-config-compat",
     "firebase-exp",
-    "@firebase/app-compat",
     "@firebase/changelog-generator",
     "firebase-size-analysis"
   ],
diff --git a/packages-exp/app-check-compat/.eslintrc.js b/packages-exp/app-check-compat/.eslintrc.js
new file mode 100644
index 00000000000..468a2ee6a34
--- /dev/null
+++ b/packages-exp/app-check-compat/.eslintrc.js
@@ -0,0 +1,33 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const path = require('path');
+
+module.exports = {
+  'extends': '../../config/.eslintrc.js',
+  'parserOptions': {
+    'project': 'tsconfig.json',
+    'tsconfigRootDir': __dirname
+  },
+  rules: {
+    'import/no-extraneous-dependencies': [
+      'error',
+      {
+        'packageDir': [path.resolve(__dirname, '../../'), __dirname]
+      }
+    ]
+  }
+};
diff --git a/packages-exp/app-check-compat/README.md b/packages-exp/app-check-compat/README.md
new file mode 100644
index 00000000000..fab8226da30
--- /dev/null
+++ b/packages-exp/app-check-compat/README.md
@@ -0,0 +1,5 @@
+# @firebase/app-check-compat
+
+This is the Firebase App Check component (compat version) of the Firebase JS SDK.
+
+**This package is not intended for direct usage, and should only be used via the officially supported [`firebase`](https://www.npmjs.com/package/firebase) package.**
diff --git a/packages-exp/app-check-compat/karma.conf.js b/packages-exp/app-check-compat/karma.conf.js
new file mode 100644
index 00000000000..324777bcd54
--- /dev/null
+++ b/packages-exp/app-check-compat/karma.conf.js
@@ -0,0 +1,32 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const karmaBase = require('../../config/karma.base');
+
+const files = [`**/*.test.ts`];
+
+module.exports = function (config) {
+  config.set({
+    ...karmaBase,
+    files,
+    preprocessors: { '**/*.ts': ['webpack', 'sourcemap'] },
+    frameworks: ['mocha']
+  });
+};
+
+module.exports.files = files;
diff --git a/packages-exp/app-check-compat/package.json b/packages-exp/app-check-compat/package.json
new file mode 100644
index 00000000000..2dc071e49e1
--- /dev/null
+++ b/packages-exp/app-check-compat/package.json
@@ -0,0 +1,60 @@
+{
+  "name": "@firebase/app-check-compat",
+  "version": "0.0.900",
+  "private": true,
+  "description": "A compat App Check package for new firebase packages",
+  "author": "Firebase <firebase-support@google.com> (https://firebase.google.com/)",
+  "main": "dist/index.cjs.js",
+  "browser": "dist/index.esm2017.js",
+  "module": "dist/index.esm2017.js",
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "lint": "eslint -c .eslintrc.js '**/*.ts' --ignore-path '../../.gitignore'",
+    "lint:fix": "eslint --fix -c .eslintrc.js '**/*.ts' --ignore-path '../../.gitignore'",
+    "build": "rollup -c",
+    "build:release": "rollup -c rollup.config.release.js",
+    "build:deps": "lerna run --scope @firebase/app-check-compat --include-dependencies build",
+    "dev": "rollup -c -w",
+    "test": "run-p lint test:browser",
+    "test:ci": "node ../../scripts/run_tests_in_ci.js -s test:browser",
+    "test:browser": "karma start --single-run --nocache"
+  },
+  "peerDependencies": {
+    "@firebase/app-compat": "0.x"
+  },
+  "dependencies": {
+    "@firebase/app-check-exp": "0.0.900",
+    "@firebase/logger": "0.2.6",
+    "@firebase/util": "1.1.0",
+    "@firebase/component": "0.5.3",
+    "tslib": "^2.1.0"
+  },
+  "license": "Apache-2.0",
+  "devDependencies": {
+    "@firebase/app-compat": "0.0.900",
+    "rollup": "2.33.2",
+    "@rollup/plugin-commonjs": "17.1.0",
+    "@rollup/plugin-json": "4.1.0",
+    "@rollup/plugin-node-resolve": "11.2.0",
+    "rollup-plugin-typescript2": "0.29.0",
+    "typescript": "4.2.2"
+  },
+  "repository": {
+    "directory": "packages/app-check",
+    "type": "git",
+    "url": "https://github.com/firebase/firebase-js-sdk.git"
+  },
+  "bugs": {
+    "url": "https://github.com/firebase/firebase-js-sdk/issues"
+  },
+  "typings": "dist/src/index.d.ts",
+  "nyc": {
+    "extension": [
+      ".ts"
+    ],
+    "reportDir": "./coverage/node"
+  },
+  "esm5": "dist/index.esm.js"
+}
\ No newline at end of file
diff --git a/packages-exp/app-check-compat/rollup.config.js b/packages-exp/app-check-compat/rollup.config.js
new file mode 100644
index 00000000000..9b89b7772af
--- /dev/null
+++ b/packages-exp/app-check-compat/rollup.config.js
@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import json from '@rollup/plugin-json';
+import typescriptPlugin from 'rollup-plugin-typescript2';
+import typescript from 'typescript';
+import { es2017BuildsNoPlugin, es5BuildsNoPlugin } from './rollup.shared';
+
+/**
+ * ES5 Builds
+ */
+const es5BuildPlugins = [
+  typescriptPlugin({
+    typescript
+  }),
+  json()
+];
+
+const es5Builds = es5BuildsNoPlugin.map(build => ({
+  ...build,
+  plugins: es5BuildPlugins
+}));
+
+/**
+ * ES2017 Builds
+ */
+const es2017BuildPlugins = [
+  typescriptPlugin({
+    typescript,
+    tsconfigOverride: {
+      compilerOptions: {
+        target: 'es2017'
+      }
+    }
+  }),
+  json({ preferConst: true })
+];
+
+const es2017Builds = es2017BuildsNoPlugin.map(build => ({
+  ...build,
+  plugins: es2017BuildPlugins
+}));
+
+export default [...es5Builds, ...es2017Builds];
diff --git a/packages-exp/app-check-compat/rollup.config.release.js b/packages-exp/app-check-compat/rollup.config.release.js
new file mode 100644
index 00000000000..1896d7036f5
--- /dev/null
+++ b/packages-exp/app-check-compat/rollup.config.release.js
@@ -0,0 +1,67 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import typescriptPlugin from 'rollup-plugin-typescript2';
+import typescript from 'typescript';
+import json from '@rollup/plugin-json';
+import { importPathTransformer } from '../../scripts/exp/ts-transform-import-path';
+import { es2017BuildsNoPlugin, es5BuildsNoPlugin } from './rollup.shared';
+
+/**
+ * ES5 Builds
+ */
+const es5BuildPlugins = [
+  typescriptPlugin({
+    typescript,
+    clean: true,
+    abortOnError: false,
+    transformers: [importPathTransformer]
+  }),
+  json()
+];
+
+const es5Builds = es5BuildsNoPlugin.map(build => ({
+  ...build,
+  plugins: es5BuildPlugins
+}));
+
+/**
+ * ES2017 Builds
+ */
+const es2017BuildPlugins = [
+  typescriptPlugin({
+    typescript,
+    tsconfigOverride: {
+      compilerOptions: {
+        target: 'es2017'
+      }
+    },
+    abortOnError: false,
+    clean: true,
+    transformers: [importPathTransformer]
+  }),
+  json({
+    preferConst: true
+  })
+];
+
+const es2017Builds = es2017BuildsNoPlugin.map(build => ({
+  ...build,
+  plugins: es2017BuildPlugins
+}));
+
+export default [...es5Builds, ...es2017Builds];
diff --git a/packages-exp/app-check-compat/rollup.shared.js b/packages-exp/app-check-compat/rollup.shared.js
new file mode 100644
index 00000000000..24bbc5a28c7
--- /dev/null
+++ b/packages-exp/app-check-compat/rollup.shared.js
@@ -0,0 +1,54 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import pkg from './package.json';
+
+const deps = [
+  ...Object.keys(Object.assign({}, pkg.peerDependencies, pkg.dependencies)),
+  '@firebase/app'
+];
+
+export const es5BuildsNoPlugin = [
+  /**
+   * Browser Builds
+   */
+  {
+    input: 'src/index.ts',
+    output: [
+      { file: pkg.main, format: 'cjs', sourcemap: true },
+      { file: pkg.esm5, format: 'es', sourcemap: true }
+    ],
+    external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
+  }
+];
+
+/**
+ * ES2017 Builds
+ */
+export const es2017BuildsNoPlugin = [
+  {
+    /**
+     * Browser Build
+     */
+    input: 'src/index.ts',
+    output: {
+      file: pkg.browser,
+      format: 'es',
+      sourcemap: true
+    },
+    external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
+  }
+];
diff --git a/packages-exp/app-check-compat/src/index.ts b/packages-exp/app-check-compat/src/index.ts
new file mode 100644
index 00000000000..d8aad99e612
--- /dev/null
+++ b/packages-exp/app-check-compat/src/index.ts
@@ -0,0 +1,69 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import firebase, {
+  _FirebaseNamespace,
+  FirebaseApp
+} from '@firebase/app-compat';
+import { name, version } from '../package.json';
+import {
+  Component,
+  ComponentContainer,
+  ComponentType,
+  InstanceFactory
+} from '@firebase/component';
+import { AppCheckService } from './service';
+import { FirebaseAppCheck } from '../../../packages/app-check-types';
+
+declare module '@firebase/component' {
+  interface NameServiceMapping {
+    'appCheck-compat': AppCheckService;
+  }
+}
+
+const factory: InstanceFactory<'appCheck-compat'> = (
+  container: ComponentContainer
+) => {
+  // Dependencies
+  const app = container.getProvider('app-compat').getImmediate();
+  const appCheckServiceExp = container
+    .getProvider('app-check-exp')
+    .getImmediate();
+
+  return new AppCheckService(app as FirebaseApp, appCheckServiceExp);
+};
+
+export function registerAppCheck(): void {
+  (firebase as _FirebaseNamespace).INTERNAL.registerComponent(
+    new Component('appCheck-compat', factory, ComponentType.PUBLIC)
+  );
+}
+
+registerAppCheck();
+firebase.registerVersion(name, version);
+
+/**
+ * Define extension behavior of `registerAppCheck`
+ */
+declare module '@firebase/app-compat' {
+  interface FirebaseNamespace {
+    appCheck(app?: FirebaseApp): FirebaseAppCheck;
+  }
+  interface FirebaseApp {
+    appCheck(): FirebaseAppCheck;
+  }
+}
diff --git a/packages-exp/app-check-compat/src/service.test.ts b/packages-exp/app-check-compat/src/service.test.ts
new file mode 100644
index 00000000000..fe6cf762426
--- /dev/null
+++ b/packages-exp/app-check-compat/src/service.test.ts
@@ -0,0 +1,142 @@
+/**
+ * @license
+ * Copyright 2017 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { expect, use } from 'chai';
+import { AppCheckService } from './service';
+import { firebase, FirebaseApp } from '@firebase/app-compat';
+import * as appCheckExp from '@firebase/app-check-exp';
+import { stub, match, SinonStub } from 'sinon';
+import * as sinonChai from 'sinon-chai';
+import { CustomProvider, ReCaptchaV3Provider } from '@firebase/app-check-exp';
+import { AppCheckTokenResult } from '../../../packages/app-check-types';
+import { PartialObserver } from '../../../packages/util/dist';
+
+use(sinonChai);
+
+function createTestService(app: FirebaseApp): AppCheckService {
+  return new AppCheckService(
+    app,
+    appCheckExp.initializeAppCheck(app, {
+      provider: new ReCaptchaV3Provider('fake-site-key')
+    })
+  );
+}
+
+describe('Firebase App Check > Service', () => {
+  let app: FirebaseApp;
+  let service: AppCheckService;
+
+  beforeEach(() => {
+    app = firebase.initializeApp({
+      apiKey: '456_LETTERS_AND_1234NUMBERS',
+      appId: '123lettersand:numbers',
+      projectId: 'my-project',
+      messagingSenderId: 'messaging-sender-id'
+    });
+  });
+
+  afterEach(async () => {
+    await app.delete();
+  });
+
+  it(
+    'activate("string") calls modular initializeAppCheck() with a ' +
+      'ReCaptchaV3Provider',
+    () => {
+      const initializeAppCheckStub = stub(appCheckExp, 'initializeAppCheck');
+      service = new AppCheckService(app, {} as appCheckExp.AppCheck);
+      service.activate('my_site_key');
+      expect(initializeAppCheckStub).to.be.calledWith(app, {
+        provider: match.instanceOf(ReCaptchaV3Provider),
+        isTokenAutoRefreshEnabled: undefined
+      });
+      initializeAppCheckStub.restore();
+    }
+  );
+
+  it(
+    'activate(CustomProvider) calls modular initializeAppCheck() with' +
+      ' a CustomProvider',
+    () => {
+      const initializeAppCheckStub = stub(appCheckExp, 'initializeAppCheck');
+      service = new AppCheckService(app, {} as appCheckExp.AppCheck);
+      const customGetTokenStub = stub();
+      service.activate({
+        getToken: customGetTokenStub
+      });
+      expect(initializeAppCheckStub).to.be.calledWith(app, {
+        provider: match
+          .instanceOf(CustomProvider)
+          .and(
+            match.hasNested(
+              '_customProviderOptions.getToken',
+              customGetTokenStub
+            )
+          ),
+        isTokenAutoRefreshEnabled: undefined
+      });
+      initializeAppCheckStub.restore();
+    }
+  );
+
+  it('setTokenAutoRefreshEnabled() calls modular setTokenAutoRefreshEnabled()', () => {
+    const setTokenAutoRefreshEnabledStub: SinonStub = stub(
+      appCheckExp,
+      'setTokenAutoRefreshEnabled'
+    );
+    service = createTestService(app);
+    service.setTokenAutoRefreshEnabled(true);
+    expect(setTokenAutoRefreshEnabledStub).to.be.calledWith(
+      service._delegate,
+      true
+    );
+    setTokenAutoRefreshEnabledStub.restore();
+  });
+
+  it('getToken() calls modular getToken()', async () => {
+    service = createTestService(app);
+    const getTokenStub = stub(appCheckExp, 'getToken');
+    await service.getToken(true);
+    expect(getTokenStub).to.be.calledWith(service._delegate, true);
+    getTokenStub.restore();
+  });
+
+  it('onTokenChanged() calls modular onTokenChanged() with observer', () => {
+    const onTokenChangedStub = stub(appCheckExp, 'onTokenChanged');
+    service = createTestService(app);
+    const observer: PartialObserver<AppCheckTokenResult> = {
+      next: stub(),
+      error: stub()
+    };
+    service.onTokenChanged(observer);
+    expect(onTokenChangedStub).to.be.calledWith(service._delegate, observer);
+    onTokenChangedStub.restore();
+  });
+
+  it('onTokenChanged() calls modular onTokenChanged() with next/error fns', () => {
+    const onTokenChangedStub = stub(appCheckExp, 'onTokenChanged');
+    service = createTestService(app);
+    const nextFn = stub();
+    const errorFn = stub();
+    service.onTokenChanged(nextFn, errorFn);
+    expect(onTokenChangedStub).to.be.calledWith(
+      service._delegate,
+      nextFn,
+      errorFn
+    );
+    onTokenChangedStub.restore();
+  });
+});
diff --git a/packages-exp/app-check-compat/src/service.ts b/packages-exp/app-check-compat/src/service.ts
new file mode 100644
index 00000000000..a64e9c67b07
--- /dev/null
+++ b/packages-exp/app-check-compat/src/service.ts
@@ -0,0 +1,79 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  AppCheckProvider,
+  AppCheckTokenResult,
+  FirebaseAppCheck
+} from '@firebase/app-check-types';
+import { _FirebaseService, FirebaseApp } from '@firebase/app-compat';
+import {
+  AppCheck as AppCheckServiceExp,
+  CustomProvider,
+  initializeAppCheck,
+  ReCaptchaV3Provider,
+  setTokenAutoRefreshEnabled as setTokenAutoRefreshEnabledExp,
+  getToken as getTokenExp,
+  onTokenChanged as onTokenChangedExp
+} from '@firebase/app-check-exp';
+import { PartialObserver, Unsubscribe } from '@firebase/util';
+
+export class AppCheckService implements FirebaseAppCheck, _FirebaseService {
+  constructor(
+    public app: FirebaseApp,
+    readonly _delegate: AppCheckServiceExp
+  ) {}
+  activate(
+    siteKeyOrProvider: string | AppCheckProvider,
+    isTokenAutoRefreshEnabled?: boolean
+  ): void {
+    let provider: ReCaptchaV3Provider | CustomProvider;
+    if (typeof siteKeyOrProvider === 'string') {
+      provider = new ReCaptchaV3Provider(siteKeyOrProvider);
+    } else {
+      provider = new CustomProvider({ getToken: siteKeyOrProvider.getToken });
+    }
+    initializeAppCheck(this.app, {
+      provider,
+      isTokenAutoRefreshEnabled
+    });
+  }
+  setTokenAutoRefreshEnabled(isTokenAutoRefreshEnabled: boolean): void {
+    setTokenAutoRefreshEnabledExp(this._delegate, isTokenAutoRefreshEnabled);
+  }
+  getToken(forceRefresh?: boolean): Promise<AppCheckTokenResult> {
+    return getTokenExp(this._delegate, forceRefresh);
+  }
+  onTokenChanged(
+    onNextOrObserver:
+      | PartialObserver<AppCheckTokenResult>
+      | ((tokenResult: AppCheckTokenResult) => void),
+    onError?: (error: Error) => void,
+    onCompletion?: () => void
+  ): Unsubscribe {
+    return onTokenChangedExp(
+      this._delegate,
+      /**
+       * Exp onTokenChanged() will handle both overloads but we need
+       * to specify one to not confuse Typescript.
+       */
+      onNextOrObserver as (tokenResult: AppCheckTokenResult) => void,
+      onError,
+      onCompletion
+    );
+  }
+}
diff --git a/packages-exp/app-check-compat/tsconfig.json b/packages-exp/app-check-compat/tsconfig.json
new file mode 100644
index 00000000000..356e7a53b8c
--- /dev/null
+++ b/packages-exp/app-check-compat/tsconfig.json
@@ -0,0 +1,8 @@
+{
+  "extends": "../../config/tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "strict": true
+  },
+  "exclude": ["dist/**/*"]
+}