diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
index 71dbcb6193..075be9efe4 100644
--- a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
@@ -326,6 +326,10 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 			}
 		}
 
+		if ( rest_is_field_included( 'is_block_theme', $fields ) ) {
+			$data['is_block_theme'] = $theme->is_block_theme();
+		}
+
 		$data = $this->add_additional_fields_to_object( $data, $request );
 
 		// Wrap the data in a response object.
@@ -494,6 +498,11 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 						),
 					),
 				),
+				'is_block_theme' => array(
+					'description' => __( 'Whether the theme is a block-based theme.' ),
+					'type'        => 'boolean',
+					'readonly'    => true,
+				),
 				'name'           => array(
 					'description' => __( 'The name of the theme.' ),
 					'type'        => 'object',
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6ffd42b459..72cff7172d 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-55950';
+$wp_version = '6.3-alpha-55951';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.