diff --git a/litellm/rerank_api/types.py b/litellm/rerank_api/types.py
index dae79f875..b4765c0e6 100644
--- a/litellm/rerank_api/types.py
+++ b/litellm/rerank_api/types.py
@@ -6,7 +6,7 @@ https://docs.cohere.com/reference/rerank
 
 from typing import List, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, PrivateAttr
 
 
 class RerankRequest(BaseModel):
@@ -23,7 +23,9 @@ class RerankResponse(BaseModel):
     id: str
     results: List[dict]  # Contains index and relevance_score
     meta: dict  # Contains api_version and billed_units
-    _hidden_params: dict = {}
+
+    # Define private attributes using PrivateAttr
+    _hidden_params: dict = PrivateAttr(default_factory=dict)
 
     def __getitem__(self, key):
         return self.__dict__[key]