diff --git a/wp-includes/post-thumbnail-template.php b/wp-includes/post-thumbnail-template.php
index 6c8fa584a1..79b9a55d3a 100644
--- a/wp-includes/post-thumbnail-template.php
+++ b/wp-includes/post-thumbnail-template.php
@@ -57,7 +57,17 @@ function get_post_thumbnail_id( $post = null ) {
 		return false;
 	}
 
-	return (int) get_post_meta( $post->ID, '_thumbnail_id', true );
+	$thumbnail_id = (int) get_post_meta( $post->ID, '_thumbnail_id', true );
+
+	/**
+	 * Filters post thumbnail ID.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param int|false        $thumbnail_id Post thumbnail ID or false if the post does not exist.
+	 * @param int|WP_Post|null $post         Post ID or WP_Post object. Default is global `$post`.
+	 */
+	return (int) apply_filters( 'post_thumbnail_id', $thumbnail_id, $post );
 }
 
 /**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b9423ad53a..a2a5857dd3 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52027';
+$wp_version = '5.9-alpha-52028';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.