diff --git a/litellm/responses/utils.py b/litellm/responses/utils.py
index cff113dc3e5..234eb777aca 100644
--- a/litellm/responses/utils.py
+++ b/litellm/responses/utils.py
@@ -204,6 +204,9 @@ class ResponsesAPIRequestUtils:
         if response_id is None:
             return responses_api_response
 
+        if ResponsesAPIRequestUtils._is_litellm_encoded_response_id(response_id):
+            return responses_api_response
+
         updated_id = ResponsesAPIRequestUtils._build_responses_api_response_id(
             model_id=model_id,
             custom_llm_provider=custom_llm_provider,
@@ -470,6 +473,14 @@ class ResponsesAPIRequestUtils:
                 response_id=response_id,
             )
 
+    @staticmethod
+    def _is_litellm_encoded_response_id(response_id: str) -> bool:
+        decoded_response_id = ResponsesAPIRequestUtils._decode_responses_api_response_id(response_id)
+        return (
+            decoded_response_id.get("model_id") is not None
+            or decoded_response_id.get("custom_llm_provider") is not None
+        )
+
     @staticmethod
     def get_model_id_from_response_id(response_id: Optional[str]) -> Optional[str]:
         """Get the model_id from the response_id"""
diff --git a/tests/test_litellm/responses/test_responses_utils.py b/tests/test_litellm/responses/test_responses_utils.py
index bd441321507..bbc137b959f 100644
--- a/tests/test_litellm/responses/test_responses_utils.py
+++ b/tests/test_litellm/responses/test_responses_utils.py
@@ -142,6 +142,26 @@ class TestResponsesAPIRequestUtils:
         assert decoded.get("model_id") == "gpt-4o"
         assert decoded.get("custom_llm_provider") == "openai"
 
+
+    def test_update_responses_api_response_id_with_model_id_is_idempotent_for_litellm_ids(self):
+        raw = "resp_" + "a" * 48
+        litellm_metadata = {"model_info": {"id": "model-123"}}
+
+        once = ResponsesAPIRequestUtils._update_responses_api_response_id_with_model_id(
+            {"id": raw},
+            custom_llm_provider="openai",
+            litellm_metadata=litellm_metadata,
+        )
+        twice = ResponsesAPIRequestUtils._update_responses_api_response_id_with_model_id(
+            {"id": once["id"]},
+            custom_llm_provider="openai",
+            litellm_metadata=litellm_metadata,
+        )
+
+        assert twice == once
+        assert ResponsesAPIRequestUtils.decode_previous_response_id_to_original_previous_response_id(twice["id"]) == raw
+        assert ResponsesAPIRequestUtils._decode_responses_api_response_id(once["id"]).get("response_id") == raw
+
     def test_build_decode_container_id_omits_none_model_id(self):
         """model_id=None must not round-trip as the truthy string 'None'."""
         encoded = ResponsesAPIRequestUtils._build_container_id(