The ThemeData.useMaterial3 flag is true by default
Summary
#The Material library has been updated to match the latest Material Design spec. Changes include new components, new component themes, and updated component visuals. As of this release, ThemeData.useMaterial3 is set true by default.
Background
#Flutter's Material widgets now fully support Material 3 and, as of Flutter 3.16, Material 3 is now the default style.
The appearance of Material 3 components are primarily determined by the values for ThemeData.colorScheme and ThemeData.textTheme. ColorScheme makes it easier to create dark and light schemes so that your app is both aesthetically pleasing and compliant with accessibility requirements. To further customize the appearance of Material 3 components, add component themes to your ThemeData, such as ThemeData.segmentedButtonTheme or ThemeData.snackBarTheme.
Additionally, Material 3 improves motion by using easing and duration tokens. This means that Material 2 curves have been renamed to include the word "legacy" and will eventually be deprecated and removed.
Check out the Material 3 gallery to test out all the new components and compare them with Material 2.
Migration guide
#Prior to the 3.16 release, the changes were "opt-in" using the useMaterial3 theme property on ThemeData. As of this release, useMaterial3 is true by default. You can still opt out of the Material 3 version of the Material library by specifying useMaterial3: false in your MaterialApp theme.
Also, some of the widgets couldn't merely be updated, but needed a whole new implementation. For this reason, your UI might look a little strange when you see it running with Material 3. To fix this, manually migrate to the new widgets, such as NavigationBar.
For more details, check out the Material 3 umbrella issue on GitHub.
Timeline
#Landed in version: 3.13.0-4.0.pre
In stable release: 3.16
References
#Documentation:
API documentation:
Relevant issues:
Relevant PRs: