diff --git a/src/wp-admin/widgets-form-blocks.php b/src/wp-admin/widgets-form-blocks.php
index 1cb1a15e1d59c..c6cb6624e8ee2 100644
--- a/src/wp-admin/widgets-form-blocks.php
+++ b/src/wp-admin/widgets-form-blocks.php
@@ -24,44 +24,7 @@
 );
 block_editor_rest_api_preload( $preload_paths, $block_editor_context );
 
-$editor_settings = get_block_editor_settings(
-	array(
-		/**
-		 * Filters the list of widget-type IDs that should **not** be offered by the
-		 * Legacy Widget block.
-		 *
-		 * Returning an empty array will make all widgets available.
-		 *
-		 * @since 5.8.0
-		 *
-		 * @param array $widgets An array of excluded widget-type IDs.
-		 */
-		'widgetTypesToHideFromLegacyWidgetBlock' => apply_filters(
-			'widget_types_to_hide_from_legacy_widget_block',
-			array(
-				'pages',
-				'calendar',
-				'archives',
-				'media_audio',
-				'media_image',
-				'media_gallery',
-				'media_video',
-				'meta',
-				'search',
-				'text',
-				'categories',
-				'recent-posts',
-				'recent-comments',
-				'rss',
-				'tag_cloud',
-				'nav_menu',
-				'custom_html',
-				'block',
-			)
-		),
-	),
-	$block_editor_context
-);
+$editor_settings = get_block_editor_settings( array(), $block_editor_context );
 
 wp_add_inline_script(
 	'wp-edit-widgets',
diff --git a/src/wp-admin/widgets.php b/src/wp-admin/widgets.php
index 1258b7049dce2..303ebb0bc97f1 100644
--- a/src/wp-admin/widgets.php
+++ b/src/wp-admin/widgets.php
@@ -23,21 +23,7 @@
 $title       = __( 'Widgets' );
 $parent_file = 'themes.php';
 
-/**
- * Filters whether or not to use the block editor to manage widgets.
- *
- * @since 5.8.0
- *
- * @param boolean $use_widgets_block_editor Whether or not to use the block editor to manage widgets.
- */
-$use_widgets_block_editor = apply_filters(
-	'use_widgets_block_editor',
-	get_theme_support( 'widgets-block-editor' )
-);
-
-$use_widgets_block_editor = true;
-
-if ( $use_widgets_block_editor ) {
+if ( wp_use_widgets_block_editor() ) {
 	require ABSPATH . 'wp-admin/widgets-form-blocks.php';
 } else {
 	require ABSPATH . 'wp-admin/widgets-form.php';
diff --git a/src/wp-includes/block-editor.php b/src/wp-includes/block-editor.php
index 8a110ccbdadbf..0fb57a280dba6 100644
--- a/src/wp-includes/block-editor.php
+++ b/src/wp-includes/block-editor.php
@@ -225,6 +225,40 @@ function get_default_block_editor_settings() {
 		$editor_settings['gradients'] = $gradient_presets;
 	}
 
+	/**
+	 * Filters the list of widget-type IDs that should **not** be offered by the
+	 * Legacy Widget block.
+	 *
+	 * Returning an empty array will make all widgets available.
+	 *
+	 * @since 5.8.0
+	 *
+	 * @param array $widgets An array of excluded widget-type IDs.
+	 */
+	$editor_settings['widgetTypesToHideFromLegacyWidgetBlock'] = apply_filters(
+		'widget_types_to_hide_from_legacy_widget_block',
+		array(
+			'pages',
+			'calendar',
+			'archives',
+			'media_audio',
+			'media_image',
+			'media_gallery',
+			'media_video',
+			'meta',
+			'search',
+			'text',
+			'categories',
+			'recent-posts',
+			'recent-comments',
+			'rss',
+			'tag_cloud',
+			'nav_menu',
+			'custom_html',
+			'block',
+		)
+	);
+
 	return $editor_settings;
 }
 
diff --git a/src/wp-includes/class-wp-customize-control.php b/src/wp-includes/class-wp-customize-control.php
index 25964fb7bc7dd..04db0d4e4c808 100644
--- a/src/wp-includes/class-wp-customize-control.php
+++ b/src/wp-includes/class-wp-customize-control.php
@@ -795,3 +795,8 @@ protected function content_template() {}
  * WP_Customize_Date_Time_Control class.
  */
 require_once ABSPATH . WPINC . '/customize/class-wp-customize-date-time-control.php';
+
+/**
+ * WP_Sidebar_Block_Editor_Control class.
+ */
+require_once ABSPATH . WPINC . '/customize/class-wp-sidebar-block-editor-control.php';
diff --git a/src/wp-includes/class-wp-customize-widgets.php b/src/wp-includes/class-wp-customize-widgets.php
index ed9bbe3dfd5e7..b2ab25601d284 100644
--- a/src/wp-includes/class-wp-customize-widgets.php
+++ b/src/wp-includes/class-wp-customize-widgets.php
@@ -118,6 +118,7 @@ public function __construct( $manager ) {
 		add_action( 'customize_controls_print_footer_scripts', array( $this, 'output_widget_control_templates' ) );
 		add_action( 'customize_preview_init', array( $this, 'customize_preview_init' ) );
 		add_filter( 'customize_refresh_nonces', array( $this, 'refresh_nonces' ) );
+		add_filter( 'should_load_block_editor_scripts_and_styles', array( $this, 'should_load_block_editor_scripts_and_styles' ) );
 
 		add_action( 'dynamic_sidebar', array( $this, 'tally_rendered_widgets' ) );
 		add_filter( 'is_active_sidebar', array( $this, 'tally_sidebars_via_is_active_sidebar_calls' ), 10, 2 );
@@ -368,6 +369,8 @@ public function schedule_customize_register() {
 	public function customize_register() {
 		global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_sidebars;
 
+		$use_widgets_block_editor = wp_use_widgets_block_editor();
+
 		add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );
 
 		$sidebars_widgets = array_merge(
@@ -446,13 +449,18 @@ public function customize_register() {
 				if ( $is_active_sidebar ) {
 
 					$section_args = array(
-						'title'       => $wp_registered_sidebars[ $sidebar_id ]['name'],
-						'description' => $wp_registered_sidebars[ $sidebar_id ]['description'],
-						'priority'    => array_search( $sidebar_id, array_keys( $wp_registered_sidebars ), true ),
-						'panel'       => 'widgets',
-						'sidebar_id'  => $sidebar_id,
+						'title'      => $wp_registered_sidebars[ $sidebar_id ]['name'],
+						'priority'   => array_search( $sidebar_id, array_keys( $wp_registered_sidebars ), true ),
+						'panel'      => 'widgets',
+						'sidebar_id' => $sidebar_id,
 					);
 
+					if ( $use_widgets_block_editor ) {
+						$section_args['description'] = '';
+					} else {
+						$section_args['description'] = $wp_registered_sidebars[ $sidebar_id ]['description'];
+					}
+
 					/**
 					 * Filters Customizer widget section arguments for a given sidebar.
 					 *
@@ -467,49 +475,63 @@ public function customize_register() {
 					$section = new WP_Customize_Sidebar_Section( $this->manager, $section_id, $section_args );
 					$this->manager->add_section( $section );
 
-					$control           = new WP_Widget_Area_Customize_Control(
-						$this->manager,
-						$setting_id,
-						array(
-							'section'    => $section_id,
-							'sidebar_id' => $sidebar_id,
-							'priority'   => count( $sidebar_widget_ids ), // place 'Add Widget' and 'Reorder' buttons at end.
-						)
-					);
-					$new_setting_ids[] = $setting_id;
+					if ( $use_widgets_block_editor ) {
+						$control = new WP_Sidebar_Block_Editor_Control(
+							$this->manager,
+							$setting_id,
+							array(
+								'section'    => $section_id,
+								'sidebar_id' => $sidebar_id,
+							)
+						);
+					} else {
+						$control = new WP_Widget_Area_Customize_Control(
+							$this->manager,
+							$setting_id,
+							array(
+								'section'    => $section_id,
+								'sidebar_id' => $sidebar_id,
+								'priority'   => count( $sidebar_widget_ids ), // place 'Add Widget' and 'Reorder' buttons at end.
+							)
+						);
+					}
 
 					$this->manager->add_control( $control );
+
+					$new_setting_ids[] = $setting_id;
 				}
 			}
 
-			// Add a control for each active widget (located in a sidebar).
-			foreach ( $sidebar_widget_ids as $i => $widget_id ) {
+			if ( ! $use_widgets_block_editor ) {
+				// Add a control for each active widget (located in a sidebar).
+				foreach ( $sidebar_widget_ids as $i => $widget_id ) {
 
-				// Skip widgets that may have gone away due to a plugin being deactivated.
-				if ( ! $is_active_sidebar || ! isset( $wp_registered_widgets[ $widget_id ] ) ) {
-					continue;
-				}
+					// Skip widgets that may have gone away due to a plugin being deactivated.
+					if ( ! $is_active_sidebar || ! isset( $wp_registered_widgets[ $widget_id ] ) ) {
+						continue;
+					}
 
-				$registered_widget = $wp_registered_widgets[ $widget_id ];
-				$setting_id        = $this->get_setting_id( $widget_id );
-				$id_base           = $wp_registered_widget_controls[ $widget_id ]['id_base'];
+					$registered_widget = $wp_registered_widgets[ $widget_id ];
+					$setting_id        = $this->get_setting_id( $widget_id );
+					$id_base           = $wp_registered_widget_controls[ $widget_id ]['id_base'];
 
-				$control = new WP_Widget_Form_Customize_Control(
-					$this->manager,
-					$setting_id,
-					array(
-						'label'          => $registered_widget['name'],
-						'section'        => $section_id,
-						'sidebar_id'     => $sidebar_id,
-						'widget_id'      => $widget_id,
-						'widget_id_base' => $id_base,
-						'priority'       => $i,
-						'width'          => $wp_registered_widget_controls[ $widget_id ]['width'],
-						'height'         => $wp_registered_widget_controls[ $widget_id ]['height'],
-						'is_wide'        => $this->is_wide_widget( $widget_id ),
-					)
-				);
-				$this->manager->add_control( $control );
+					$control = new WP_Widget_Form_Customize_Control(
+						$this->manager,
+						$setting_id,
+						array(
+							'label'          => $registered_widget['name'],
+							'section'        => $section_id,
+							'sidebar_id'     => $sidebar_id,
+							'widget_id'      => $widget_id,
+							'widget_id_base' => $id_base,
+							'priority'       => $i,
+							'width'          => $wp_registered_widget_controls[ $widget_id ]['width'],
+							'height'         => $wp_registered_widget_controls[ $widget_id ]['height'],
+							'is_wide'        => $this->is_wide_widget( $widget_id ),
+						)
+					);
+					$this->manager->add_control( $control );
+				}
 			}
 		}
 
@@ -805,6 +827,46 @@ public function enqueue_scripts() {
 			'data',
 			sprintf( 'var _wpCustomizeWidgetsSettings = %s;', wp_json_encode( $settings ) )
 		);
+
+		// TODO: Update 'wp-customize-widgets' to not rely so much on things in
+		// 'customize-widgets'. This will let us skip most of the above and not
+		// enqueue 'customize-widgets' which saves bytes.
+
+		if ( wp_use_widgets_block_editor() ) {
+			$block_editor_context = new WP_Block_Editor_Context();
+
+			$editor_settings = get_block_editor_settings( array(), $block_editor_context );
+
+			wp_add_inline_script(
+				'wp-customize-widgets',
+				sprintf(
+					'wp.domReady( function() {
+					   wp.customizeWidgets.initialize( "widgets-customizer", %s );
+					} );',
+					wp_json_encode( $editor_settings )
+				)
+			);
+
+			// Preload server-registered block schemas.
+			wp_add_inline_script(
+				'wp-blocks',
+				'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+			);
+
+			wp_add_inline_script(
+				'wp-blocks',
+				sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( 'widgets-customizer' ) ) ),
+				'after'
+			);
+
+			wp_enqueue_script( 'wp-customize-widgets' );
+			wp_enqueue_style( 'wp-customize-widgets' );
+			wp_enqueue_script( 'wp-format-library' );
+			wp_enqueue_style( 'wp-format-library' );
+
+			/** This action is documented in edit-form-blocks.php */
+			do_action( 'enqueue_block_editor_assets' );
+		}
 	}
 
 	/**
@@ -888,8 +950,13 @@ public function get_setting_args( $id, $overrides = array() ) {
 			$args['sanitize_js_callback'] = array( $this, 'sanitize_sidebar_widgets_js_instance' );
 			$args['transport']            = current_theme_supports( 'customize-selective-refresh-widgets' ) ? 'postMessage' : 'refresh';
 		} elseif ( preg_match( $this->setting_id_patterns['widget_instance'], $id, $matches ) ) {
-			$args['sanitize_callback']    = array( $this, 'sanitize_widget_instance' );
-			$args['sanitize_js_callback'] = array( $this, 'sanitize_widget_js_instance' );
+			$id_base                      = $matches['id_base'];
+			$args['sanitize_callback']    = function( $value ) use ( $id_base ) {
+				return $this->sanitize_widget_instance( $value, $id_base );
+			};
+			$args['sanitize_js_callback'] = function( $value ) use ( $id_base ) {
+				return $this->sanitize_widget_js_instance( $value, $id_base );
+			};
 			$args['transport']            = $this->is_widget_selective_refreshable( $matches['id_base'] ) ? 'postMessage' : 'refresh';
 		}
 
@@ -1108,6 +1175,23 @@ public function refresh_nonces( $nonces ) {
 		return $nonces;
 	}
 
+	/**
+	 * Tells the script loader to load the scripts and styles of custom blocks
+	 * if the widgets block editor is enabled.
+	 *
+	 * @since 5.8.0
+	 *
+	 * @param bool $is_block_editor_screen Current decision about loading block assets.
+	 * @return bool Filtered decision about loading block assets.
+	 */
+	public function should_load_block_editor_scripts_and_styles( $is_block_editor_screen ) {
+		if ( wp_use_widgets_block_editor() ) {
+			return true;
+		}
+
+		return $is_block_editor_screen;
+	}
+
 	/**
 	 * When previewing, ensures the proper previewing widgets are used.
 	 *
@@ -1314,16 +1398,28 @@ protected function get_instance_hash_key( $serialized_instance ) {
 	 * @since 3.9.0
 	 *
 	 * @param array $value Widget instance to sanitize.
+	 * @param string $id_base Base of the ID of the widget being sanitized.
 	 * @return array|void Sanitized widget instance.
 	 */
-	public function sanitize_widget_instance( $value ) {
+	public function sanitize_widget_instance( $value, $id_base = null ) {
+		global $wp_widget_factory;
+
 		if ( array() === $value ) {
-			return $value;
+			return;
 		}
 
-		if ( empty( $value['is_widget_customizer_js_value'] )
-			|| empty( $value['instance_hash_key'] )
-			|| empty( $value['encoded_serialized_instance'] ) ) {
+		if ( isset( $value['raw_instance'] ) && $id_base && wp_use_widgets_block_editor() ) {
+			$widget_object = $wp_widget_factory->get_widget_object( $id_base );
+			if ( ! empty( $widget_object->widget_options['show_instance_in_rest'] ) ) {
+				return $value['raw_instance'];
+			}
+		}
+
+		if (
+			empty( $value['is_widget_customizer_js_value'] ) ||
+			empty( $value['instance_hash_key'] ) ||
+			empty( $value['encoded_serialized_instance'] )
+		) {
 			return;
 		}
 
@@ -1350,19 +1446,32 @@ public function sanitize_widget_instance( $value ) {
 	 * @since 3.9.0
 	 *
 	 * @param array $value Widget instance to convert to JSON.
+	 * @param string $id_base Base of the ID of the widget being sanitized.
 	 * @return array JSON-converted widget instance.
 	 */
-	public function sanitize_widget_js_instance( $value ) {
+	public function sanitize_widget_js_instance( $value, $id_base = null ) {
+		global $wp_widget_factory;
+
 		if ( empty( $value['is_widget_customizer_js_value'] ) ) {
 			$serialized = serialize( $value );
 
-			$value = array(
+			$js_value = array(
 				'encoded_serialized_instance'   => base64_encode( $serialized ),
 				'title'                         => empty( $value['title'] ) ? '' : $value['title'],
 				'is_widget_customizer_js_value' => true,
 				'instance_hash_key'             => $this->get_instance_hash_key( $serialized ),
 			);
+
+			if ( $id_base && wp_use_widgets_block_editor() ) {
+				$widget_object = $wp_widget_factory->get_widget_object( $id_base );
+				if ( ! empty( $widget_object->widget_options['show_instance_in_rest'] ) ) {
+					$js_value['raw_instance'] = (object) $value;
+				}
+			}
+
+			return $js_value;
 		}
+
 		return $value;
 	}
 
@@ -1432,7 +1541,7 @@ public function call_widget_update( $widget_id ) {
 				return new WP_Error( 'widget_setting_malformed' );
 			}
 
-			$instance = $this->sanitize_widget_instance( $sanitized_widget_setting );
+			$instance = $this->sanitize_widget_instance( $sanitized_widget_setting, $parsed_id['id_base'] );
 			if ( is_null( $instance ) ) {
 				$this->stop_capturing_option_updates();
 				return new WP_Error( 'widget_setting_unsanitized' );
@@ -1498,7 +1607,7 @@ public function call_widget_update( $widget_id ) {
 		 * in place from WP_Customize_Setting::preview() will use this value
 		 * instead of the default widget instance value (an empty array).
 		 */
-		$this->manager->set_post_value( $setting_id, $this->sanitize_widget_js_instance( $instance ) );
+		$this->manager->set_post_value( $setting_id, $this->sanitize_widget_js_instance( $instance, $parsed_id['id_base'] ) );
 
 		// Obtain the widget control with the updated instance in place.
 		ob_start();
@@ -1571,7 +1680,7 @@ public function wp_ajax_update_widget() {
 		}
 
 		$form     = $updated_widget['form'];
-		$instance = $this->sanitize_widget_js_instance( $updated_widget['instance'] );
+		$instance = $this->sanitize_widget_js_instance( $updated_widget['instance'], $id_base );
 
 		wp_send_json_success( compact( 'form', 'instance' ) );
 	}
diff --git a/src/wp-includes/customize/class-wp-sidebar-block-editor-control.php b/src/wp-includes/customize/class-wp-sidebar-block-editor-control.php
new file mode 100644
index 0000000000000..a2d1e4bc78b1b
--- /dev/null
+++ b/src/wp-includes/customize/class-wp-sidebar-block-editor-control.php
@@ -0,0 +1,37 @@
+<?php
+/**
+ * Customize API: WP_Sidebar_Block_Editor_Control class.
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 5.8.0
+ */
+
+/**
+ * Core class used to implement the widgets block editor control in the
+ * customizer.
+ *
+ * @since 5.8.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Sidebar_Block_Editor_Control extends WP_Customize_Control {
+	/**
+	 * The control type.
+	 *
+	 * @since 5.8.0
+	 *
+	 * @var string
+	 */
+	public $type = 'sidebar_block_editor';
+
+	/**
+	 * Render the widgets block editor container.
+	 *
+	 * @since 5.8.0
+	 */
+	public function render_content() {
+		// Render an empty control. The JavaScript in
+		// @wordpress/customize-widgets will do the rest.
+	}
+}
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 62b12b9bd3d0c..40b9695f55ddf 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -1556,6 +1556,14 @@ function wp_default_styles( $styles ) {
 			'wp-block-editor',
 			'wp-edit-blocks',
 			'wp-block-library',
+			'wp-reusable-blocks',
+		),
+		'customize-widgets'    => array(
+			'wp-components',
+			'wp-block-editor',
+			'wp-edit-blocks',
+			'wp-block-library',
+			'wp-reusable-blocks',
 		),
 	);
 
diff --git a/src/wp-includes/widgets.php b/src/wp-includes/widgets.php
index c044215e07eef..ba6aea7a6ba34 100644
--- a/src/wp-includes/widgets.php
+++ b/src/wp-includes/widgets.php
@@ -1801,6 +1801,8 @@ function wp_widgets_init() {
 
 	register_widget( 'WP_Widget_Block' );
 
+	add_theme_support( 'widgets-block-editor' );
+
 	/**
 	 * Fires after all default WordPress widgets have been registered.
 	 *
@@ -1809,6 +1811,27 @@ function wp_widgets_init() {
 	do_action( 'widgets_init' );
 }
 
+/**
+ * Whether or not to use the block editor to manage widgets. Defaults to true
+ * unless a theme has removed support for widgets-block-editor or a plugin has
+ * filtered the return value of this function.
+ *
+ * @since 5.8.0
+ *
+ * @return boolean Whether or not to use the block editor to manage widgets.
+ */
+function wp_use_widgets_block_editor() {
+	/**
+	 * Filters whether or not to use the block editor to manage widgets.
+	 *
+	 * @param boolean $use_widgets_block_editor Whether or not to use the block editor to manage widgets.
+	 */
+	return apply_filters(
+		'use_widgets_block_editor',
+		get_theme_support( 'widgets-block-editor' )
+	);
+}
+
 /**
  * Converts a widget ID into its id_base and number components.
  *
diff --git a/tests/phpunit/includes/functions.php b/tests/phpunit/includes/functions.php
index 7e409d5fce1ad..b8274c0a115d1 100644
--- a/tests/phpunit/includes/functions.php
+++ b/tests/phpunit/includes/functions.php
@@ -310,6 +310,7 @@ function _unhook_block_registration() {
 	remove_action( 'init', 'register_block_core_loginout' );
 	remove_action( 'init', 'register_block_core_latest_comments' );
 	remove_action( 'init', 'register_block_core_latest_posts' );
+	remove_action( 'init', 'register_block_core_legacy_widget', 20 );
 	remove_action( 'init', 'register_block_core_post_author' );
 	remove_action( 'init', 'register_block_core_post_content' );
 	remove_action( 'init', 'register_block_core_post_date' );
diff --git a/tests/phpunit/tests/blocks/block-editor.php b/tests/phpunit/tests/blocks/block-editor.php
index b11ac707c8933..896a1ae36fd05 100644
--- a/tests/phpunit/tests/blocks/block-editor.php
+++ b/tests/phpunit/tests/blocks/block-editor.php
@@ -159,7 +159,7 @@ function test_get_allowed_block_types_deprecated_filter_post_editor() {
 	function test_get_default_block_editor_settings() {
 		$settings = get_default_block_editor_settings();
 
-		$this->assertCount( 16, $settings );
+		$this->assertCount( 17, $settings );
 		$this->assertFalse( $settings['alignWide'] );
 		$this->assertInternalType( 'array', $settings['allowedMimeTypes'] );
 		$this->assertTrue( $settings['allowedBlockTypes'] );
@@ -254,6 +254,29 @@ function test_get_default_block_editor_settings() {
 			$settings['imageSizes']
 		);
 		$this->assertInternalType( 'int', $settings['maxUploadFileSize'] );
+		$this->assertSameSets(
+			array(
+				'archives',
+				'block',
+				'calendar',
+				'categories',
+				'custom_html',
+				'media_audio',
+				'media_gallery',
+				'media_image',
+				'media_video',
+				'meta',
+				'nav_menu',
+				'pages',
+				'recent-comments',
+				'recent-posts',
+				'rss',
+				'search',
+				'tag_cloud',
+				'text',
+			),
+			$settings['widgetTypesToHideFromLegacyWidgetBlock']
+		);
 	}
 
 	/**
diff --git a/tests/phpunit/tests/customize/widgets.php b/tests/phpunit/tests/customize/widgets.php
index 46ab3f81b5da7..19bf9772be3c8 100644
--- a/tests/phpunit/tests/customize/widgets.php
+++ b/tests/phpunit/tests/customize/widgets.php
@@ -25,6 +25,7 @@ function setUp() {
 		require_once ABSPATH . WPINC . '/class-wp-customize-manager.php';
 
 		add_theme_support( 'customize-selective-refresh-widgets' );
+		add_action( 'widgets_init', array( $this, 'remove_widgets_block_editor' ) );
 		$user_id = self::factory()->user->create( array( 'role' => 'administrator' ) );
 		wp_set_current_user( $user_id );
 		$GLOBALS['wp_customize'] = new WP_Customize_Manager();
@@ -85,6 +86,10 @@ function do_customize_boot_actions() {
 		do_action( 'wp', $GLOBALS['wp'] );
 	}
 
+	function remove_widgets_block_editor() {
+		remove_theme_support( 'widgets-block-editor' );
+	}
+
 	/**
 	 * Test WP_Customize_Widgets::__construct()
 	 */
@@ -258,31 +263,31 @@ function test_get_setting_args() {
 		add_filter( 'widget_customizer_setting_args', array( $this, 'filter_widget_customizer_setting_args' ), 10, 2 );
 
 		$default_args = array(
-			'type'                 => 'option',
-			'capability'           => 'edit_theme_options',
-			'transport'            => 'refresh',
-			'default'              => array(),
-			'sanitize_callback'    => array( $this->manager->widgets, 'sanitize_widget_instance' ),
-			'sanitize_js_callback' => array( $this->manager->widgets, 'sanitize_widget_js_instance' ),
+			'type'       => 'option',
+			'capability' => 'edit_theme_options',
+			'transport'  => 'refresh',
+			'default'    => array(),
 		);
 		$args         = $this->manager->widgets->get_setting_args( 'widget_foo[2]' );
 		foreach ( $default_args as $key => $default_value ) {
 			$this->assertSame( $default_value, $args[ $key ] );
 		}
+		$this->assertTrue( is_callable( $args['sanitize_callback'] ), 'sanitize_callback is callable' );
+		$this->asserttrue( is_callable( $args['sanitize_js_callback'] ), 'sanitize_js_callback is callable' );
 		$this->assertSame( 'WIDGET_FOO[2]', $args['uppercase_id_set_by_filter'] );
 
 		$default_args = array(
-			'type'                 => 'option',
-			'capability'           => 'edit_theme_options',
-			'transport'            => 'postMessage',
-			'default'              => array(),
-			'sanitize_callback'    => array( $this->manager->widgets, 'sanitize_widget_instance' ),
-			'sanitize_js_callback' => array( $this->manager->widgets, 'sanitize_widget_js_instance' ),
+			'type'       => 'option',
+			'capability' => 'edit_theme_options',
+			'transport'  => 'postMessage',
+			'default'    => array(),
 		);
 		$args         = $this->manager->widgets->get_setting_args( 'widget_search[2]' );
 		foreach ( $default_args as $key => $default_value ) {
 			$this->assertSame( $default_value, $args[ $key ] );
 		}
+		$this->assertTrue( is_callable( $args['sanitize_callback'] ), 'sanitize_callback is callable' );
+		$this->asserttrue( is_callable( $args['sanitize_js_callback'] ), 'sanitize_js_callback is callable' );
 
 		remove_theme_support( 'customize-selective-refresh-widgets' );
 		$args = $this->manager->widgets->get_setting_args( 'widget_search[2]' );
@@ -304,17 +309,17 @@ function test_get_setting_args() {
 		$this->assertSame( 'WIDGET_BAR[3]', $args['uppercase_id_set_by_filter'] );
 
 		$default_args = array(
-			'type'                 => 'option',
-			'capability'           => 'edit_theme_options',
-			'transport'            => 'postMessage',
-			'default'              => array(),
-			'sanitize_callback'    => array( $this->manager->widgets, 'sanitize_sidebar_widgets' ),
-			'sanitize_js_callback' => array( $this->manager->widgets, 'sanitize_sidebar_widgets_js_instance' ),
+			'type'       => 'option',
+			'capability' => 'edit_theme_options',
+			'transport'  => 'postMessage',
+			'default'    => array(),
 		);
 		$args         = $this->manager->widgets->get_setting_args( 'sidebars_widgets[sidebar-1]' );
 		foreach ( $default_args as $key => $default_value ) {
 			$this->assertSame( $default_value, $args[ $key ] );
 		}
+		$this->assertTrue( is_callable( $args['sanitize_callback'] ), 'sanitize_callback is callable' );
+		$this->asserttrue( is_callable( $args['sanitize_js_callback'] ), 'sanitize_js_callback is callable' );
 		$this->assertSame( 'SIDEBARS_WIDGETS[SIDEBAR-1]', $args['uppercase_id_set_by_filter'] );
 
 		$override_args = array(