diff -r 48c4eec2b7e6 -r 8c2e4d02f4ef wp/wp-includes/block-supports/block-style-variations.php
--- a/wp/wp-includes/block-supports/block-style-variations.php	Fri Sep 05 18:40:08 2025 +0200
+++ b/wp/wp-includes/block-supports/block-style-variations.php	Fri Sep 05 18:52:52 2025 +0200
@@ -8,21 +8,6 @@
  */
 
 /**
- * Generate block style variation instance name.
- *
- * @since 6.6.0
- * @access private
- *
- * @param array  $block     Block object.
- * @param string $variation Slug for the block style variation.
- *
- * @return string The unique variation name.
- */
-function wp_create_block_style_variation_instance_name( $block, $variation ) {
-	return $variation . '--' . md5( serialize( $block ) );
-}
-
-/**
  * Determines the block style variation names within a CSS class string.
  *
  * @since 6.6.0
@@ -77,7 +62,7 @@
 	}
 }
 /**
- * Render the block style variation's styles.
+ * Renders the block style variation's styles.
  *
  * In the case of nested blocks with variations applied, we want the parent
  * variation's styles to be rendered before their descendants. This solves the
@@ -124,7 +109,7 @@
 	 */
 	wp_resolve_block_style_variation_ref_values( $variation_data, $theme_json );
 
-	$variation_instance = wp_create_block_style_variation_instance_name( $parsed_block, $variation );
+	$variation_instance = wp_unique_id( $variation . '--' );
 	$class_name         = "is-style-$variation_instance";
 	$updated_class_name = $parsed_block['attrs']['className'] . " $class_name";
 
@@ -209,15 +194,15 @@
 }
 
 /**
- * Ensure the variation block support class name generated and added to
+ * Ensures the variation block support class name generated and added to
  * block attributes in the `render_block_data` filter gets applied to the
  * block's markup.
  *
- * @see wp_render_block_style_variation_support_styles
- *
  * @since 6.6.0
  * @access private
  *
+ * @see wp_render_block_style_variation_support_styles
+ *
  * @param  string $block_content Rendered block content.
  * @param  array  $block         Block object.
  *
@@ -230,11 +215,9 @@
 
 	/*
 	 * Matches a class prefixed by `is-style`, followed by the
-	 * variation slug, then `--`, and finally a hash.
-	 *
-	 * See `wp_create_block_style_variation_instance_name` for class generation.
+	 * variation slug, then `--`, and finally an instance number.
 	 */
-	preg_match( '/\bis-style-(\S+?--\w+)\b/', $block['attrs']['className'], $matches );
+	preg_match( '/\bis-style-(\S+?--\d+)\b/', $block['attrs']['className'], $matches );
 
 	if ( empty( $matches ) ) {
 		return $block_content;