Index: src/wp-includes/meta.php
===================================================================
--- src/wp-includes/meta.php	(revision 43140)
+++ src/wp-includes/meta.php	(working copy)
@@ -952,6 +952,18 @@
 function is_protected_meta( $meta_key, $meta_type = null ) {
 	$protected = ( '_' == $meta_key[0] );
 
+	if( $meta_type ) {
+		/**
+		 * Filters whether a meta key is considered protected.
+		 *
+		 * @since 5.0.0
+		 *
+		 * @param bool $protected Whether the key is considered protected.
+		 * @param string $meta_key Meta key.
+		 * @param string|null $meta_type Type of object metadata is for (e.g., comment, post, or user).
+		 */
+		$protected = apply_filters( "protected_{$meta_type}_meta_{$meta_key}", $protected, $meta_key, $meta_type );
+	}
 	/**
 	 * Filters whether a meta key is considered protected.
 	 *
@@ -1026,10 +1038,13 @@
 		$wp_meta_keys = array();
 	}
 
+	$protected = ( '_' == $meta_key[0] );
+
 	$defaults = array(
 		'type'              => 'string',
 		'description'       => '',
 		'single'            => false,
+		'protected'         => $protected,
 		'sanitize_callback' => null,
 		'auth_callback'     => null,
 		'show_in_rest'      => false,
@@ -1067,6 +1082,15 @@
 	$args = apply_filters( 'register_meta_args', $args, $defaults, $object_type, $meta_key );
 	$args = wp_parse_args( $args, $defaults );
 
+	if ( $protected ) {
+		$protected_callback = "__return_true";
+	} else {
+		$protected_callback = "__return_false";
+	}
+
+	add_filter( "protected_{$meta_type}_meta_{$meta_key}", $protected_callback, 8, 1 );
+
+
 	// If `auth_callback` is not provided, fall back to `is_protected_meta()`.
 	if ( empty( $args['auth_callback'] ) ) {
 		if ( is_protected_meta( $meta_key, $object_type ) ) {
@@ -1149,6 +1173,15 @@
 		remove_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'] );
 	}
 
+	if ( isset( $args['protected'] )  ) {
+		if ( $args['protected'] ) {
+			$protected_callback = "__return_true";
+		} else {
+			$protected_callback = "__return_false";
+		}
+		remove_filter( "protected_{$object_type}_meta_{$meta_key}", $protected_callback, 8 );
+	}
+
 	unset( $wp_meta_keys[ $object_type ][ $meta_key ] );
 
 	// Do some clean up