diff --git a/wp-admin/includes/admin-filters.php b/wp-admin/includes/admin-filters.php
index e80c111dde..33354cb073 100644
--- a/wp-admin/includes/admin-filters.php
+++ b/wp-admin/includes/admin-filters.php
@@ -80,6 +80,7 @@ add_filter( 'heartbeat_received', 'wp_refresh_post_lock', 10, 3 );
 add_filter( 'heartbeat_received', 'heartbeat_autosave', 500, 2 );
 
 add_filter( 'wp_refresh_nonces', 'wp_refresh_post_nonces', 10, 3 );
+add_filter( 'wp_refresh_nonces', 'wp_refresh_metabox_loader_nonces', 10, 2 );
 add_filter( 'wp_refresh_nonces', 'wp_refresh_heartbeat_nonces' );
 
 add_filter( 'heartbeat_settings', 'wp_heartbeat_set_suspension' );
diff --git a/wp-admin/includes/misc.php b/wp-admin/includes/misc.php
index 94337fee7d..65cf69ab31 100644
--- a/wp-admin/includes/misc.php
+++ b/wp-admin/includes/misc.php
@@ -1255,6 +1255,41 @@ function wp_refresh_post_nonces( $response, $data, $screen_id ) {
 	return $response;
 }
 
+/**
+ * Refresh nonces used with meta boxes in the block editor.
+ *
+ * @since 6.1.0
+ *
+ * @param array  $response  The Heartbeat response.
+ * @param array  $data      The $_POST data sent.
+ * @return array The Heartbeat response.
+ */
+function wp_refresh_metabox_loader_nonces( $response, $data ) {
+	if ( empty( $data['wp-refresh-metabox-loader-nonces'] ) ) {
+		return $response;
+	}
+
+	$received = $data['wp-refresh-metabox-loader-nonces'];
+	$post_id  = (int) $received['post_id'];
+
+	if ( ! $post_id ) {
+		return $response;
+	}
+
+	if ( ! current_user_can( 'edit_post', $post_id ) ) {
+		return $response;
+	}
+
+	$response['wp-refresh-metabox-loader-nonces'] = array(
+		'replace' => array(
+			'metabox_loader_nonce' => wp_create_nonce( 'meta-box-loader' ),
+			'_wpnonce'             => wp_create_nonce( 'update-post_' . $post_id ),
+		),
+	);
+
+	return $response;
+}
+
 /**
  * Adds the latest Heartbeat and REST-API nonce to the Heartbeat response.
  *
diff --git a/wp-admin/includes/post.php b/wp-admin/includes/post.php
index 8eb0368220..1abe542316 100644
--- a/wp-admin/includes/post.php
+++ b/wp-admin/includes/post.php
@@ -2334,6 +2334,50 @@ function the_block_editor_meta_boxes() {
 		wp_add_inline_script( 'wp-lists', $script );
 	}
 
+	/*
+	 * Refresh nonces used by the meta box loader.
+	 *
+	 * The logic is very similar to that provided by post.js for the classic editor.
+	 */
+	$script = "( function( $ ) {
+		var check, timeout;
+
+		function schedule() {
+			check = false;
+			window.clearTimeout( timeout );
+			timeout = window.setTimeout( function() { check = true; }, 300000 );
+		}
+
+		$( document ).on( 'heartbeat-send.wp-refresh-nonces', function( e, data ) {
+			var post_id, \$authCheck = $( '#wp-auth-check-wrap' );
+
+			if ( check || ( \$authCheck.length && ! \$authCheck.hasClass( 'hidden' ) ) ) {
+				if ( ( post_id = $( '#post_ID' ).val() ) && $( '#_wpnonce' ).val() ) {
+					data['wp-refresh-metabox-loader-nonces'] = {
+						post_id: post_id
+					};
+				}
+			}
+		}).on( 'heartbeat-tick.wp-refresh-nonces', function( e, data ) {
+			var nonces = data['wp-refresh-metabox-loader-nonces'];
+
+			if ( nonces ) {
+				if ( nonces.replace ) {
+					if ( nonces.replace.metabox_loader_nonce && window._wpMetaBoxUrl && wp.url ) {
+						window._wpMetaBoxUrl= wp.url.addQueryArgs( window._wpMetaBoxUrl, { 'meta-box-loader-nonce': nonces.replace.metabox_loader_nonce } );
+					}
+
+					if ( nonces.replace._wpnonce ) {
+						$( '#_wpnonce' ).val( nonces.replace._wpnonce );
+					}
+				}
+			}
+		}).ready( function() {
+			schedule();
+		});
+	} )( jQuery );";
+	wp_add_inline_script( 'heartbeat', $script );
+
 	// Reset meta box data.
 	$wp_meta_boxes = $_original_meta_boxes;
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index bdd6a421ea..01b7aebdec 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-54121';
+$wp_version = '6.1-alpha-54122';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.