wp-includes/theme.php:4355Returns whether the active theme is a block-based theme or not.
boolfunction wp_is_block_theme() { if ( empty( $GLOBALS['wp_theme_directories'] ) ) { _doing_it_wrong( __FUNCTION__, __( 'This function should not be called before the theme directory is registered.' ), '6.8.0' ); return false; } return wp_get_theme()->is_block_theme();}Introduced in 5.9.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/theme.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.