diff --git a/wp-includes/block-template-utils.php b/wp-includes/block-template-utils.php
index c5953e1d4c..94934599a8 100644
--- a/wp-includes/block-template-utils.php
+++ b/wp-includes/block-template-utils.php
@@ -549,15 +549,18 @@ function _build_block_template_result_from_file( $template_file, $template_type
 		$template->area = $template_file['area'];
 	}
 
-	$before_block_visitor = '_inject_theme_attribute_in_template_part_block';
+	$before_block_visitor = ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ? '_inject_theme_attribute_in_template_part_block' : null;
 	$after_block_visitor  = null;
 	$hooked_blocks        = get_hooked_blocks();
 	if ( ! empty( $hooked_blocks ) || has_filter( 'hooked_block_types' ) ) {
 		$before_block_visitor = make_before_block_visitor( $hooked_blocks, $template );
 		$after_block_visitor  = make_after_block_visitor( $hooked_blocks, $template );
 	}
-	$blocks            = parse_blocks( $template_content );
-	$template->content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+	if ( null !== $before_block_visitor || null !== $after_block_visitor ) {
+		$blocks           = parse_blocks( $template_content );
+		$template_content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+	}
+	$template->content = $template_content;
 
 	return $template;
 }
diff --git a/wp-includes/blocks.php b/wp-includes/blocks.php
index ecb4fa5b3d..3a2e943ad5 100644
--- a/wp-includes/blocks.php
+++ b/wp-includes/blocks.php
@@ -779,7 +779,9 @@ function make_before_block_visitor( $hooked_blocks, $context ) {
 	 * @return string The serialized markup for the given block, with the markup for any hooked blocks prepended to it.
 	 */
 	return function ( &$block, $parent_block = null, $prev = null ) use ( $hooked_blocks, $context ) {
-		_inject_theme_attribute_in_template_part_block( $block );
+		if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
+			_inject_theme_attribute_in_template_part_block( $block );
+		}
 
 		$markup = '';
 
diff --git a/wp-includes/class-wp-block-patterns-registry.php b/wp-includes/class-wp-block-patterns-registry.php
index a11bac06be..1c528abb3f 100644
--- a/wp-includes/class-wp-block-patterns-registry.php
+++ b/wp-includes/class-wp-block-patterns-registry.php
@@ -165,14 +165,16 @@ final class WP_Block_Patterns_Registry {
 	private function prepare_content( $pattern, $hooked_blocks ) {
 		$content = $pattern['content'];
 
-		$before_block_visitor = '_inject_theme_attribute_in_template_part_block';
+		$before_block_visitor = ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ? '_inject_theme_attribute_in_template_part_block' : null;
 		$after_block_visitor  = null;
 		if ( ! empty( $hooked_blocks ) || has_filter( 'hooked_block_types' ) ) {
 			$before_block_visitor = make_before_block_visitor( $hooked_blocks, $pattern );
 			$after_block_visitor  = make_after_block_visitor( $hooked_blocks, $pattern );
 		}
-		$blocks  = parse_blocks( $content );
-		$content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+		if ( null !== $before_block_visitor || null !== $after_block_visitor ) {
+			$blocks  = parse_blocks( $content );
+			$content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+		}
 
 		return $content;
 	}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 52d81d0510..cc43927789 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-beta3-56849';
+$wp_version = '6.4-beta3-56896';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.