Making Material 3 the default is the last big step in our long (long) transition from Material 2 to Material 3. Currently apps must opt-in to Material 3 with the useMaterial3 flag that appears in all of the ThemeData factory constructors.

  return MaterialApp(
    theme: ThemeData(useMaterial3: true),
    // ...
  );

Once this issue has been resolved, useMaterial3: true will be the default. It will still be possible to configure applications for Material 2 by specifying useMaterial3: false.

Once this change has landed in a stable release, the useMaterial3 flag will be deprecated and eventually removed per Flutter's deprecation policy.

#129724 Exists to ensure that the the Flutter repo doesn't regress. There's a similar CL for Google internal tests: cl/543770414.

Step 1 - All tests pass when useMaterial3 is true by default

Tests that do not pass when useMaterial is temporarily set to true by default in theme_data.dart (roughly line #442) will either be split into a pair of tests, one that specifies M3 and one that specifies M2, or a single provisional test that specifies M2. For the latter, the test should be added to Step 3 below.

• Dev, examples/api, etc updated for Material 3 by default #129683
• Update golden tests #128914
• Update golden tests for material #128839
• Update tests in material library for Material 3 by default #128300
• Update misc tests for Material3 #128712
• Update unit tests in material library for Material 3 #128725
• Update rest of the unit tests in material library for Material 3 #128747
• Update button tests for Material 3 by default #128628
• Updated material button theme tests for Material3 #128543
• Updated flutter_localizations tests for Material3; #128521
• Use Material3 in the 2D viewport tests #128155
• Updated TabBar and ToggleButtons examples #128088
• Updated Menu examples #128080
• Updated custom ListTile examples #128071
• Updated InputDecoratorExamples for M3 #128065
• Revised Floating Action Button examples #128058
• Update tests in material library for Material 3 by default #128300
• Updated chip_test.dart tests for M3 #129570
• Updated dashboard: wired down Material2 dependency cocoon#2837
• Updated widget_test and enhanced_composited_transform_test: wired down Material2 dependency fzyzcjy/flutter_portal#103
• Update one floating cursor test for the M3 default transition superlistapp/super_editor#1173
• Updated dashboard/test/widgets tests to handle useMaterial3:true by default cocoon#2846
• Updated rfw/test/material_widgets_test.dart for M3 packages#4316

Step 2 - ThemeData useMaterial3 is true by default

• Change the default forThemeData.useMaterial3 to true #129724
• Updated ThemeData.useMaterial3 API doc, default is true #130764

Step 3 - Add M2 and M3-specific tests

-- The remaining work for Step 3 has been moved to #139076 --

Tests that were modified with useMaterial3: false will likely need an M3 version. Examples that were modified with useMaterial3: false should be updated (along with their tests) to M3.

A list of all the test files that are likely to need to be updated can be found in the M2-M3 Updates TODO spreadsheet.