diff --git a/wp-includes/block-editor.php b/wp-includes/block-editor.php
index 007c713190..2bd9f2dfbf 100644
--- a/wp-includes/block-editor.php
+++ b/wp-includes/block-editor.php
@@ -856,3 +856,21 @@ function get_classic_theme_supports_block_editor_settings() {
 
 	return $theme_settings;
 }
+
+/**
+ * Initialize site preview.
+ *
+ * This function sets IFRAME_REQUEST to true if the site preview parameter is set.
+ *
+ * @since 6.8.0
+ */
+function wp_initialize_site_preview_hooks() {
+	if (
+		! defined( 'IFRAME_REQUEST' ) &&
+		isset( $_GET['wp_site_preview'] ) &&
+		1 === (int) $_GET['wp_site_preview'] &&
+		current_user_can( 'edit_theme_options' )
+	) {
+		define( 'IFRAME_REQUEST', true );
+	}
+}
diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index d143652dd8..f6d80b091c 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -551,6 +551,9 @@ add_action( 'transition_post_status', '_wp_keep_alive_customize_changeset_depend
 // Block Theme Previews.
 add_action( 'plugins_loaded', 'wp_initialize_theme_preview_hooks', 1 );
 
+// Site preview for Classic Theme.
+add_action( 'init', 'wp_initialize_site_preview_hooks', 1 );
+
 // Calendar widget cache.
 add_action( 'save_post', 'delete_get_calendar_cache' );
 add_action( 'delete_post', 'delete_get_calendar_cache' );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 37b8b4854b..32dd229614 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.8-beta2-59993';
+$wp_version = '6.8-beta2-60003';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.