diff --git a/packages/playwright-test/src/testType.ts b/packages/playwright-test/src/testType.ts
index 71633c1ede..e30c6c2607 100644
--- a/packages/playwright-test/src/testType.ts
+++ b/packages/playwright-test/src/testType.ts
@@ -52,7 +52,7 @@ export class TestTypeImpl {
     test.step = wrapFunctionWithLocation(this._step.bind(this));
     test.use = wrapFunctionWithLocation(this._use.bind(this));
     test.extend = wrapFunctionWithLocation(this._extend.bind(this));
-    test.extendTest = wrapFunctionWithLocation(this._extendTest.bind(this));
+    test._extendTest = wrapFunctionWithLocation(this._extendTest.bind(this));
     test.info = () => {
       const result = currentTestInfo();
       if (!result)
@@ -203,7 +203,7 @@ export class TestTypeImpl {
 
   private _extend(location: Location, fixtures: Fixtures) {
     if ((fixtures as any)[testTypeSymbol])
-      throw new Error(`test.extend() accepts fixtures object, not a test object.\nDid you mean to call test.extendTest()?`);
+      throw new Error(`test.extend() accepts fixtures object, not a test object.\nDid you mean to call test._extendTest()?`);
     const fixturesWithLocation: FixturesWithLocation = { fixtures, location };
     return new TestTypeImpl([...this.fixtures, fixturesWithLocation]).test;
   }
@@ -211,7 +211,7 @@ export class TestTypeImpl {
   private _extendTest(location: Location, test: TestType<any, any>) {
     const testTypeImpl = (test as any)[testTypeSymbol] as TestTypeImpl;
     if (!testTypeImpl)
-      throw new Error(`test.extendTest() accepts a single "test" parameter.\nDid you mean to call test.extend() with fixtures instead?`);
+      throw new Error(`test._extendTest() accepts a single "test" parameter.\nDid you mean to call test.extend() with fixtures instead?`);
     // Filter out common ancestor fixtures.
     const newFixtures = testTypeImpl.fixtures.filter(theirs => !this.fixtures.find(ours => ours.fixtures === theirs.fixtures));
     return new TestTypeImpl([...this.fixtures, ...newFixtures]).test;
diff --git a/packages/playwright-test/types/test.d.ts b/packages/playwright-test/types/test.d.ts
index 2c834cbaa3..c47f5261e4 100644
--- a/packages/playwright-test/types/test.d.ts
+++ b/packages/playwright-test/types/test.d.ts
@@ -2598,7 +2598,6 @@ export interface TestType<TestArgs extends KeyValue, WorkerArgs extends KeyValue
    * @param fixtures An object containing fixtures and/or options. Learn more about [fixtures format](https://playwright.dev/docs/test-fixtures).
    */
   extend<T, W extends KeyValue = {}>(fixtures: Fixtures<T, W, TestArgs, WorkerArgs>): TestType<TestArgs & T, WorkerArgs & W>;
-  extendTest<T, W>(other: TestType<T, W>): TestType<TestArgs & T, WorkerArgs & W>;
   /**
    * Returns information about the currently running test. This method can only be called during the test execution,
    * otherwise it throws.
diff --git a/tests/config/baseTest.ts b/tests/config/baseTest.ts
index 84f27a63bc..bddb5a6e80 100644
--- a/tests/config/baseTest.ts
+++ b/tests/config/baseTest.ts
@@ -14,19 +14,27 @@
  * limitations under the License.
  */
 
-import { test } from '@playwright/test';
+import { test, TestType, Fixtures } from '@playwright/test';
 import { commonFixtures, CommonFixtures } from './commonFixtures';
 import { serverTest } from './serverFixtures';
 import { coverageTest } from './coverageFixtures';
 import { platformTest } from './platformFixtures';
 import { testModeTest } from './testModeFixtures';
 
-export const baseTest = test
-    .extendTest(coverageTest)
-    .extendTest(platformTest)
-    .extendTest(testModeTest)
+interface TestTypeEx<TestArgs, WorkerArgs> extends TestType<TestArgs, WorkerArgs> {
+  extend<T, W = {}>(fixtures: Fixtures<T, W, TestArgs, WorkerArgs>): TestTypeEx<TestArgs & T, WorkerArgs & W>;
+  _extendTest<T, W>(other: TestType<T, W>): TestTypeEx<TestArgs & T, WorkerArgs & W>;
+}
+type BaseT = (typeof test) extends TestType<infer T, infer W> ? T : never; // eslint-disable-line
+type BaseW = (typeof test) extends TestType<infer T, infer W> ? W : never; // eslint-disable-line
+export const base = test as TestTypeEx<BaseT, BaseW>;
+
+export const baseTest = base
+    ._extendTest(coverageTest)
+    ._extendTest(platformTest)
+    ._extendTest(testModeTest)
     .extend<CommonFixtures>(commonFixtures)
-    .extendTest(serverTest)
+    ._extendTest(serverTest)
     .extend<{}, { _snapshotSuffix: string }>({
       _snapshotSuffix: ['', { scope: 'worker' }],
     });
diff --git a/tests/playwright-test/test-extend.spec.ts b/tests/playwright-test/test-extend.spec.ts
index 3b9a377b74..85704980f2 100644
--- a/tests/playwright-test/test-extend.spec.ts
+++ b/tests/playwright-test/test-extend.spec.ts
@@ -181,7 +181,7 @@ test('test.extend should be able to merge', async ({ runInlineTest }) => {
         fixture2: ({}, use) => use('fixture2'),
       });
 
-      const test3 = test1.extendTest(test2);
+      const test3 = test1._extendTest(test2);
 
       test3('merged', async ({ param, fixture1, myFixture, fixture2 }) => {
         console.log('param-' + param);
@@ -199,7 +199,7 @@ test('test.extend should be able to merge', async ({ runInlineTest }) => {
   expect(result.output).toContain('fixture2-fixture2');
 });
 
-test('test.extend should print nice message when used as extendTest', async ({ runInlineTest }) => {
+test('test.extend should print nice message when used as _extendTest', async ({ runInlineTest }) => {
   const result = await runInlineTest({
     'a.test.js': `
       const test1 = pwt.test.extend({});
@@ -211,13 +211,13 @@ test('test.extend should print nice message when used as extendTest', async ({ r
   });
   expect(result.exitCode).toBe(1);
   expect(result.passed).toBe(0);
-  expect(result.output).toContain('Did you mean to call test.extendTest()?');
+  expect(result.output).toContain('Did you mean to call test._extendTest()?');
 });
 
-test('test.extendTest should print nice message when used as extend', async ({ runInlineTest }) => {
+test('test._extendTest should print nice message when used as extend', async ({ runInlineTest }) => {
   const result = await runInlineTest({
     'a.test.js': `
-      const test3 = pwt.test.extendTest({});
+      const test3 = pwt.test._extendTest({});
       test3('test', () => {});
     `,
   });
diff --git a/tests/playwright-test/types-2.spec.ts b/tests/playwright-test/types-2.spec.ts
index 0d1b6965f0..589529a3a6 100644
--- a/tests/playwright-test/types-2.spec.ts
+++ b/tests/playwright-test/types-2.spec.ts
@@ -81,7 +81,9 @@ test('test.extend options should check types', async ({ runTSC }) => {
         // @ts-expect-error
         bar: async ({ baz }, run) => { await run(42); }
       });
-      export const test4 = test1.extendTest(test1b);
+      // TODO: enable when _extendTest is out of experiment.
+      // export const test4 = test1._extendTest(test1b);
+      export const test4 = test1;
     `,
     'playwright.config.ts': `
       import { Params } from './helper';
@@ -114,7 +116,8 @@ test('test.extend options should check types', async ({ runTSC }) => {
       test2('my test', async ({ foo, bar }) => {});
       // @ts-expect-error
       test2('my test', async ({ foo, baz }) => {});
-      test4('my test', async ({ foo, bar }) => {});
+      // TODO: enable when _extendTest is out of experiment.
+      // test4('my test', async ({ foo, bar }) => {});
     `
   });
   expect(result.exitCode).toBe(0);
diff --git a/utils/generate_types/overrides-test.d.ts b/utils/generate_types/overrides-test.d.ts
index b81cef0998..808e9efe17 100644
--- a/utils/generate_types/overrides-test.d.ts
+++ b/utils/generate_types/overrides-test.d.ts
@@ -266,7 +266,6 @@ export interface TestType<TestArgs extends KeyValue, WorkerArgs extends KeyValue
   step(title: string, body: () => Promise<any>): Promise<any>;
   expect: Expect;
   extend<T, W extends KeyValue = {}>(fixtures: Fixtures<T, W, TestArgs, WorkerArgs>): TestType<TestArgs & T, WorkerArgs & W>;
-  extendTest<T, W>(other: TestType<T, W>): TestType<TestArgs & T, WorkerArgs & W>;
   info(): TestInfo;
 }