diff --git a/docs/designers-developers/developers/backward-compatibility/deprecations.md b/docs/designers-developers/developers/backward-compatibility/deprecations.md
index 294ce5aa300a1c..e94e46d6d06303 100644
--- a/docs/designers-developers/developers/backward-compatibility/deprecations.md
+++ b/docs/designers-developers/developers/backward-compatibility/deprecations.md
@@ -22,6 +22,10 @@ The Gutenberg project's deprecation policy is intended to support backward compa
 - The PHP function `gutenberg_silence_rest_errors` has been removed.
 - The PHP function `gutenberg_filter_post_type_labels` has been removed.
 - The PHP function `gutenberg_prepare_blocks_for_js` has been removed. Use [`get_block_editor_server_block_settings`](https://developer.wordpress.org/reference/functions/get_block_editor_server_block_settings/) instead.
+- The PHP function `gutenberg_remove_wpcom_markdown_support` has been removed.
+- The PHP function `gutenberg_bulk_post_updated_messages` has been removed.
+- The PHP function `gutenberg_kses_allowedtags` has been removed.
+- The PHP function `gutenberg_add_responsive_body_class` has been removed.
 
 ## 4.5.0
 - `Dropdown.refresh()` has been deprecated as the contained `Popover` is now automatically refreshed.
diff --git a/gutenberg.php b/gutenberg.php
index 655e883859fda6..7e019de8b8a252 100644
--- a/gutenberg.php
+++ b/gutenberg.php
@@ -187,10 +187,6 @@ function gutenberg_pre_init() {
 
 	require_once dirname( __FILE__ ) . '/lib/load.php';
 
-	if ( function_exists( 'gutenberg_silence_rest_errors' ) ) {
-		gutenberg_silence_rest_errors();
-	}
-
 	add_filter( 'replace_editor', 'gutenberg_init', 10, 2 );
 }
 
@@ -531,33 +527,29 @@ function gutenberg_add_admin_body_class( $classes ) {
  * Adds attributes to kses allowed tags that aren't in the default list
  * and that Gutenberg needs to save blocks such as the Gallery block.
  *
+ * @deprecated 5.0.0
+ *
  * @param array $tags Allowed HTML.
  * @return array (Maybe) modified allowed HTML.
  */
 function gutenberg_kses_allowedtags( $tags ) {
-	if ( isset( $tags['img'] ) ) {
-		$tags['img']['data-link'] = true;
-		$tags['img']['data-id']   = true;
-	}
+	_deprecated_function( __FUNCTION__, '5.0.0' );
+
 	return $tags;
 }
 
-add_filter( 'wp_kses_allowed_html', 'gutenberg_kses_allowedtags', 10, 2 );
-
 /**
  * Adds the wp-embed-responsive class to the body tag if the theme has opted in to
  * Gutenberg responsive embeds.
  *
  * @since 4.1.0
+ * @deprecated 5.0.0
  *
  * @param Array $classes Array of classes being added to the body tag.
  * @return Array The $classes array, with wp-embed-responsive appended.
  */
 function gutenberg_add_responsive_body_class( $classes ) {
-	if ( current_theme_supports( 'responsive-embeds' ) ) {
-		$classes[] = 'wp-embed-responsive';
-	}
+	_deprecated_function( __FUNCTION__, '5.0.0' );
+
 	return $classes;
 }
-
-add_filter( 'body_class', 'gutenberg_add_responsive_body_class' );
diff --git a/lib/plugin-compat.php b/lib/plugin-compat.php
index 963535624de4c3..74f6dbb2cb0c89 100644
--- a/lib/plugin-compat.php
+++ b/lib/plugin-compat.php
@@ -21,14 +21,13 @@
  * plugins Jetpack, JP-Markdown, and WP Editor.MD
  *
  * @since 1.3.0
+ * @deprecated 5.0.0
  *
  * @param  array $post      Post object which contains content to check for block.
  * @return array $post      Post object.
  */
 function gutenberg_remove_wpcom_markdown_support( $post ) {
-	if ( class_exists( 'WPCom_Markdown' ) && has_blocks( $post['post_content'] ) ) {
-		WPCom_Markdown::get_instance()->unload_markdown_for_posts();
-	}
+	_deprecated_function( __FUNCTION__, '5.0.0' );
+
 	return $post;
 }
-add_filter( 'wp_insert_post_data', 'gutenberg_remove_wpcom_markdown_support', 9 );
diff --git a/lib/register.php b/lib/register.php
index b86df4fd7a37f0..3dc7264a9dfb0e 100644
--- a/lib/register.php
+++ b/lib/register.php
@@ -538,31 +538,18 @@ function gutenberg_register_post_types() {
  * Apply the correct labels for Reusable Blocks in the bulk action updated messages.
  *
  * @since 4.3.0
+ * @deprecated 5.0.0
  *
- * @param array $messages    Arrays of messages, each keyed by the corresponding post type.
- * @param array $bulk_counts Array of item counts for each message, used to build internationalized strings.
+ * @param array $messages Arrays of messages, each keyed by the corresponding post type.
  *
  * @return array
  */
-function gutenberg_bulk_post_updated_messages( $messages, $bulk_counts ) {
-	$messages['wp_block'] = array(
-		// translators: Number of blocks updated.
-		'updated'   => _n( '%s block updated.', '%s blocks updated.', $bulk_counts['updated'], 'gutenberg' ),
-		// translators: Blocks not updated because they're locked.
-		'locked'    => ( 1 == $bulk_counts['locked'] ) ? __( '1 block not updated, somebody is editing it.', 'gutenberg' ) : _n( '%s block not updated, somebody is editing it.', '%s blocks not updated, somebody is editing them.', $bulk_counts['locked'], 'gutenberg' ),
-		// translators: Number of blocks deleted.
-		'deleted'   => _n( '%s block permanently deleted.', '%s blocks permanently deleted.', $bulk_counts['deleted'], 'gutenberg' ),
-		// translators: Number of blocks trashed.
-		'trashed'   => _n( '%s block moved to the Trash.', '%s blocks moved to the Trash.', $bulk_counts['trashed'], 'gutenberg' ),
-		// translators: Number of blocks untrashed.
-		'untrashed' => _n( '%s block restored from the Trash.', '%s blocks restored from the Trash.', $bulk_counts['untrashed'], 'gutenberg' ),
-	);
+function gutenberg_bulk_post_updated_messages( $messages ) {
+	_deprecated_function( __FUNCTION__, '5.0.0' );
 
 	return $messages;
 }
 
-add_filter( 'bulk_post_updated_messages', 'gutenberg_bulk_post_updated_messages', 10, 2 );
-
 /**
  * Injects a hidden input in the edit form to propagate the information that classic editor is selected.
  *
diff --git a/packages/block-library/src/categories/edit.js b/packages/block-library/src/categories/edit.js
index b67eb0982e0bf2..5341ad6ff51682 100644
--- a/packages/block-library/src/categories/edit.js
+++ b/packages/block-library/src/categories/edit.js
@@ -57,8 +57,7 @@ class CategoriesEdit extends Component {
 	}
 
 	getCategoryListClassName( level ) {
-		const { className } = this.props;
-		return `${ className }__list ${ className }__list-level-${ level }`;
+		return `wp-block-categories__list wp-block-categories__list-level-${ level }`;
 	}
 
 	renderCategoryName( category ) {
@@ -89,7 +88,7 @@ class CategoriesEdit extends Component {
 			<li key={ category.id }>
 				<a href={ category.link } target="_blank">{ this.renderCategoryName( category ) }</a>
 				{ showPostCounts &&
-					<span className={ `${ this.props.className }__post-count` }>
+					<span className="wp-block-categories__post-count">
 						{ ' ' }({ category.count })
 					</span>
 				}
@@ -107,7 +106,7 @@ class CategoriesEdit extends Component {
 	}
 
 	renderCategoryDropdown() {
-		const { showHierarchy, instanceId, className } = this.props;
+		const { showHierarchy, instanceId } = this.props;
 		const parentId = showHierarchy ? 0 : null;
 		const categories = this.getCategories( parentId );
 		const selectId = `blocks-category-select-${ instanceId }`;
@@ -116,7 +115,7 @@ class CategoriesEdit extends Component {
 				<label htmlFor={ selectId } className="screen-reader-text">
 					{ __( 'Categories' ) }
 				</label>
-				<select id={ selectId } className={ `${ className }__dropdown` }>
+				<select id={ selectId } className="wp-block-categories__dropdown">
 					{ categories.map( ( category ) => this.renderCategoryDropdownItem( category, 0 ) ) }
 				</select>
 			</Fragment>
diff --git a/packages/edit-post/src/components/header/feature-toggle/index.js b/packages/edit-post/src/components/header/feature-toggle/index.js
index 3b811e653fac41..c2de21f3ba713e 100644
--- a/packages/edit-post/src/components/header/feature-toggle/index.js
+++ b/packages/edit-post/src/components/header/feature-toggle/index.js
@@ -1,16 +1,30 @@
+/**
+ * External dependencies
+ */
+import { flow } from 'lodash';
+
 /**
  * WordPress Dependencies
  */
 import { withSelect, withDispatch } from '@wordpress/data';
 import { compose } from '@wordpress/compose';
-import { MenuItem } from '@wordpress/components';
+import { MenuItem, withSpokenMessages } from '@wordpress/components';
+import { __ } from '@wordpress/i18n';
+
+function FeatureToggle( { onToggle, isActive, label, info, messageActivated, messageDeactivated, speak } ) {
+	const speakMessage = () => {
+		if ( isActive ) {
+			speak( messageDeactivated || __( 'Feature deactivated' ) );
+		} else {
+			speak( messageActivated || __( 'Feature activated' ) );
+		}
+	};
 
-function FeatureToggle( { onToggle, isActive, label, info } ) {
 	return (
 		<MenuItem
 			icon={ isActive && 'yes' }
 			isSelected={ isActive }
-			onClick={ onToggle }
+			onClick={ flow( onToggle, speakMessage ) }
 			role="menuitemcheckbox"
 			label={ label }
 			info={ info }
@@ -30,4 +44,5 @@ export default compose( [
 			ownProps.onToggle();
 		},
 	} ) ),
+	withSpokenMessages,
 ] )( FeatureToggle );
diff --git a/packages/edit-post/src/components/header/writing-menu/index.js b/packages/edit-post/src/components/header/writing-menu/index.js
index e7b9c3dc791ade..6a3b6f62c44828 100644
--- a/packages/edit-post/src/components/header/writing-menu/index.js
+++ b/packages/edit-post/src/components/header/writing-menu/index.js
@@ -19,17 +19,26 @@ function WritingMenu( { onClose } ) {
 				feature="fixedToolbar"
 				label={ __( 'Top Toolbar' ) }
 				info={ __( 'Access all block and document tools in a single place' ) }
-				onToggle={ onClose } />
+				onToggle={ onClose }
+				messageActivated={ __( 'Top toolbar activated' ) }
+				messageDeactivated={ __( 'Top toolbar deactivated' ) }
+			/>
 			<FeatureToggle
 				feature="focusMode"
 				label={ __( 'Spotlight Mode' ) }
 				info={ __( 'Focus on one block at a time' ) }
-				onToggle={ onClose } />
+				onToggle={ onClose }
+				messageActivated={ __( 'Spotlight mode activated' ) }
+				messageDeactivated={ __( 'Spotlight mode deactivated' ) }
+			/>
 			<FeatureToggle
 				feature="fullscreenMode"
 				label={ __( 'Fullscreen Mode' ) }
 				info={ __( 'Work without distraction' ) }
-				onToggle={ onClose } />
+				onToggle={ onClose }
+				messageActivated={ __( 'Fullscreen mode activated' ) }
+				messageDeactivated={ __( 'Fullscreen mode deactivated' ) }
+			/>
 		</MenuGroup>
 	);
 }