diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index 71c901a0b0e..e69f6d2bd88 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -774,7 +774,7 @@ def _without_authorization(
 
 
 def _is_gateway_attribution_header(header_name: str) -> bool:
-    return header_name.lower() in {"x-litellm-tags", "x-litellm-end-user-id"}
+    return header_name.lower() in frozenset(("x-litellm-tags", "x-litellm-end-user-id"))
 
 
 def _format_byok_openapi_auth_header(mcp_server: MCPServer, mcp_auth_header: str) -> str:
diff --git a/litellm/proxy/_experimental/mcp_server/server.py b/litellm/proxy/_experimental/mcp_server/server.py
index 92a971ac758..de9dbd4ee89 100644
--- a/litellm/proxy/_experimental/mcp_server/server.py
+++ b/litellm/proxy/_experimental/mcp_server/server.py
@@ -788,8 +788,10 @@ if MCP_AVAILABLE:
 
             request_tags: Final = LiteLLMProxyRequestSetup.add_request_tag_to_metadata(
                 llm_router=None,
-                headers={key.lower(): value for key, value in (raw_headers or {}).items()},
-                data={},
+                headers={  # mutable-ok: request-tag helper accepts a mutable header mapping
+                    key.lower(): value for key, value in (raw_headers or {}).items()
+                },
+                data={},  # mutable-ok: request-tag helper mutates request metadata in place
             )
             listing: Final = await _list_mcp_tools(
                 user_api_key_auth=user_api_key_auth,