diff --git a/wp-admin/edit-form-advanced.php b/wp-admin/edit-form-advanced.php
index 6be549ad3a..1908f5c5e3 100644
--- a/wp-admin/edit-form-advanced.php
+++ b/wp-admin/edit-form-advanced.php
@@ -244,7 +244,7 @@ $post_type_object = get_post_type_object( $post_type );
 require_once( ABSPATH . 'wp-admin/includes/meta-boxes.php' );
 
 
-$publish_callback_args = null;
+$publish_callback_args = array( '__back_compat_meta_box' => true );
 if ( post_type_supports( $post_type, 'revisions' ) && 'auto-draft' != $post->post_status ) {
 	$revisions = wp_get_post_revisions( $post_ID );
 
@@ -252,28 +252,29 @@ if ( post_type_supports( $post_type, 'revisions' ) && 'auto-draft' != $post->pos
 	if ( count( $revisions ) > 1 ) {
 		reset( $revisions ); // Reset pointer for key()
 		$publish_callback_args = array(
-			'revisions_count' => count( $revisions ),
-			'revision_id'     => key( $revisions ),
+			'revisions_count'        => count( $revisions ),
+			'revision_id'            => key( $revisions ),
+			'__back_compat_meta_box' => true,
 		);
-		add_meta_box( 'revisionsdiv', __( 'Revisions' ), 'post_revisions_meta_box', null, 'normal', 'core' );
+		add_meta_box( 'revisionsdiv', __( 'Revisions' ), 'post_revisions_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 	}
 }
 
 if ( 'attachment' == $post_type ) {
 	wp_enqueue_script( 'image-edit' );
 	wp_enqueue_style( 'imgareaselect' );
-	add_meta_box( 'submitdiv', __( 'Save' ), 'attachment_submit_meta_box', null, 'side', 'core' );
+	add_meta_box( 'submitdiv', __( 'Save' ), 'attachment_submit_meta_box', null, 'side', 'core', array( '__back_compat_meta_box' => true ) );
 	add_action( 'edit_form_after_title', 'edit_form_image_editor' );
 
 	if ( wp_attachment_is( 'audio', $post ) ) {
-		add_meta_box( 'attachment-id3', __( 'Metadata' ), 'attachment_id3_data_meta_box', null, 'normal', 'core' );
+		add_meta_box( 'attachment-id3', __( 'Metadata' ), 'attachment_id3_data_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 	}
 } else {
 	add_meta_box( 'submitdiv', __( 'Publish' ), 'post_submit_meta_box', null, 'side', 'core', $publish_callback_args );
 }
 
 if ( current_theme_supports( 'post-formats' ) && post_type_supports( $post_type, 'post-formats' ) ) {
-	add_meta_box( 'formatdiv', _x( 'Format', 'post format' ), 'post_format_meta_box', null, 'side', 'core' );
+	add_meta_box( 'formatdiv', _x( 'Format', 'post format' ), 'post_format_meta_box', null, 'side', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 // all taxonomies
@@ -291,27 +292,38 @@ foreach ( get_object_taxonomies( $post ) as $tax_name ) {
 		$tax_meta_box_id = $tax_name . 'div';
 	}
 
-	add_meta_box( $tax_meta_box_id, $label, $taxonomy->meta_box_cb, null, 'side', 'core', array( 'taxonomy' => $tax_name ) );
+	add_meta_box(
+		$tax_meta_box_id,
+		$label,
+		$taxonomy->meta_box_cb,
+		null,
+		'side',
+		'core',
+		array(
+			'taxonomy'               => $tax_name,
+			'__back_compat_meta_box' => true,
+		)
+	);
 }
 
 if ( post_type_supports( $post_type, 'page-attributes' ) || count( get_page_templates( $post ) ) > 0 ) {
-	add_meta_box( 'pageparentdiv', $post_type_object->labels->attributes, 'page_attributes_meta_box', null, 'side', 'core' );
+	add_meta_box( 'pageparentdiv', $post_type_object->labels->attributes, 'page_attributes_meta_box', null, 'side', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 if ( $thumbnail_support && current_user_can( 'upload_files' ) ) {
-	add_meta_box( 'postimagediv', esc_html( $post_type_object->labels->featured_image ), 'post_thumbnail_meta_box', null, 'side', 'low' );
+	add_meta_box( 'postimagediv', esc_html( $post_type_object->labels->featured_image ), 'post_thumbnail_meta_box', null, 'side', 'low', array( '__back_compat_meta_box' => true ) );
 }
 
 if ( post_type_supports( $post_type, 'excerpt' ) ) {
-	add_meta_box( 'postexcerpt', __( 'Excerpt' ), 'post_excerpt_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'postexcerpt', __( 'Excerpt' ), 'post_excerpt_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 if ( post_type_supports( $post_type, 'trackbacks' ) ) {
-	add_meta_box( 'trackbacksdiv', __( 'Send Trackbacks' ), 'post_trackback_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'trackbacksdiv', __( 'Send Trackbacks' ), 'post_trackback_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 if ( post_type_supports( $post_type, 'custom-fields' ) ) {
-	add_meta_box( 'postcustom', __( 'Custom Fields' ), 'post_custom_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'postcustom', __( 'Custom Fields' ), 'post_custom_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 /**
@@ -327,7 +339,7 @@ do_action( 'dbx_post_advanced', $post );
 // Allow the Discussion meta box to show up if the post type supports comments,
 // or if comments or pings are open.
 if ( comments_open( $post ) || pings_open( $post ) || post_type_supports( $post_type, 'comments' ) ) {
-	add_meta_box( 'commentstatusdiv', __( 'Discussion' ), 'post_comment_status_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'commentstatusdiv', __( 'Discussion' ), 'post_comment_status_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 $stati = get_post_stati( array( 'public' => true ) );
@@ -340,16 +352,16 @@ if ( in_array( get_post_status( $post ), $stati ) ) {
 	// If the post type support comments, or the post has comments, allow the
 	// Comments meta box.
 	if ( comments_open( $post ) || pings_open( $post ) || $post->comment_count > 0 || post_type_supports( $post_type, 'comments' ) ) {
-		add_meta_box( 'commentsdiv', __( 'Comments' ), 'post_comment_meta_box', null, 'normal', 'core' );
+		add_meta_box( 'commentsdiv', __( 'Comments' ), 'post_comment_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 	}
 }
 
 if ( ! ( 'pending' == get_post_status( $post ) && ! current_user_can( $post_type_object->cap->publish_posts ) ) ) {
-	add_meta_box( 'slugdiv', __( 'Slug' ), 'post_slug_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'slugdiv', __( 'Slug' ), 'post_slug_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 if ( post_type_supports( $post_type, 'author' ) && current_user_can( $post_type_object->cap->edit_others_posts ) ) {
-	add_meta_box( 'authordiv', __( 'Author' ), 'post_author_meta_box', null, 'normal', 'core' );
+	add_meta_box( 'authordiv', __( 'Author' ), 'post_author_meta_box', null, 'normal', 'core', array( '__back_compat_meta_box' => true ) );
 }
 
 /**
diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index 75b92889e7..a1cd160076 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -1136,6 +1136,28 @@ function do_meta_boxes( $screen, $context, $object ) {
 					if ( false == $box || ! $box['title'] ) {
 						continue;
 					}
+
+					// Don't show boxes in the block editor, if they're just here for back compat.
+					if ( $screen->is_block_editor() && isset( $box['args']['__back_compat_meta_box'] ) && $box['args']['__back_compat_meta_box'] ) {
+						continue;
+					}
+
+					// Don't show boxes in the block editor that aren't compatible with the block editor.
+					if ( $screen->is_block_editor() && isset( $box['args']['__block_editor_compatible_meta_box'] ) && ! $box['args']['__block_editor_compatible_meta_box'] ) {
+						continue;
+					}
+
+					$block_compatible = true;
+					if ( isset( $box['args']['__block_editor_compatible_meta_box'] ) ) {
+						$block_compatible = (bool) $box['args']['__block_editor_compatible_meta_box'];
+						unset( $box['args']['__block_editor_compatible_meta_box'] );
+					}
+
+					if ( isset( $box['args']['__back_compat_meta_box'] ) ) {
+						$block_compatible |= (bool) $box['args']['__back_compat_meta_box'];
+						unset( $box['args']['__back_compat_meta_box'] );
+					}
+
 					$i++;
 					$hidden_class = in_array( $box['id'], $hidden ) ? ' hide-if-js' : '';
 					echo '<div id="' . $box['id'] . '" class="postbox ' . postbox_classes( $box['id'], $page ) . $hidden_class . '" ' . '>' . "\n";
@@ -1161,6 +1183,42 @@ function do_meta_boxes( $screen, $context, $object ) {
 					echo "<span>{$box['title']}</span>";
 					echo "</h2>\n";
 					echo '<div class="inside">' . "\n";
+
+					if ( WP_DEBUG && ! $screen->is_block_editor() && ! isset( $_GET['meta-box-loader'] ) ) {
+						if ( is_array( $box['callback'] ) ) {
+							$reflection = new ReflectionMethod( $box['callback'][0], $box['callback'][1] );
+						} else {
+							$reflection = new ReflectionFunction( $box['callback'] );
+						}
+
+						// Don't show an error if it's an internal PHP function.
+						if ( ! $reflection->isInternal() ) {
+
+							// Only show errors if the meta box was registered by a plugin.
+							$filename = $reflection->getFileName();
+							if ( strpos( $filename, WP_PLUGIN_DIR ) === 0 ) {
+								$filename = str_replace( WP_PLUGIN_DIR, '', $filename );
+								$filename = preg_replace( '|^/([^/]*/).*$|', '\\1', $filename );
+
+								$plugins = get_plugins();
+								foreach ( $plugins as $name => $plugin ) {
+									if ( strpos( $name, $filename ) === 0 ) {
+										?>
+											<div class="error inline">
+												<p>
+													<?php
+														/* translators: %s: the name of the plugin that generated this meta box. */
+														printf( __( "This meta box, from the %s plugin, isn't compatible with the block editor." ), "<strong>{$plugin['Name']}</strong>" );
+													?>
+												</p>
+											</div>
+										<?php
+									}
+								}
+							}
+						}
+					}
+
 					call_user_func( $box['callback'], $object, $box );
 					echo "</div>\n";
 					echo "</div>\n";
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 80cb519849..d1812099a9 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44131';
+$wp_version = '5.1-alpha-44132';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.