diff --git a/CHANGELOG.md b/CHANGELOG.md
index bee883f90..6e8b12958 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,8 @@ a release.
 ---
 
 ## [Unreleased]
+### Changed
+- All: Removed the dollar sign from the generated cache ID for extension metadata to ensure only characters mandated by [PSR-6](https://www.php-fig.org/psr/psr-6/#definitions) are used, improving compatibility with caching implementations with strict character requirements (#2978)
 
 ## [3.21.0] - 2025-09-22
 ### Added
diff --git a/src/Mapping/ExtensionMetadataFactory.php b/src/Mapping/ExtensionMetadataFactory.php
index 16d321cc3..2e4d045b4 100644
--- a/src/Mapping/ExtensionMetadataFactory.php
+++ b/src/Mapping/ExtensionMetadataFactory.php
@@ -181,7 +181,7 @@ public function getExtensionMetadata($meta)
      */
     public static function getCacheId($className, $extensionNamespace)
     {
-        return str_replace('\\', '_', $className).'_$'.strtoupper(str_replace('\\', '_', $extensionNamespace)).'_CLASSMETADATA';
+        return str_replace('\\', '_', $className).'__'.strtoupper(str_replace('\\', '_', $extensionNamespace)).'_CLASSMETADATA';
     }
 
     /**