diff --git a/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py b/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
index 641f7410126..f754c558c87 100644
--- a/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
+++ b/litellm/llms/anthropic/experimental_pass_through/messages/transformation.py
@@ -137,7 +137,7 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
         return False
 
     @staticmethod
-    def _strip_claude_code_identity_from_system(system_param):
+    def _strip_claude_code_identity_from_system(system_param) -> str | list | None:
         """
         Strip Claude Code's self-identification sentence from system parameter.