diff --git a/litellm/responses/litellm_completion_transformation/streaming_iterator.py b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
index ad6cf09aaae..f71ff3c6660 100644
--- a/litellm/responses/litellm_completion_transformation/streaming_iterator.py
+++ b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
@@ -91,8 +91,10 @@ class LiteLLMCompletionStreamingIterator(ResponsesAPIStreamingIterator):
         self.custom_llm_provider: str | None = custom_llm_provider
         self.litellm_metadata: dict | None = litellm_metadata or {}
         _wrapper_hidden_params: Final = getattr(litellm_custom_stream_wrapper, "_hidden_params", None)
-        self._hidden_params: dict[str, object] = (
-            dict(_wrapper_hidden_params) if isinstance(_wrapper_hidden_params, dict) else {}
+        self._hidden_params: dict[str, object] = (  # mutable-ok: downstream response metadata requires a mutable dict
+            dict(_wrapper_hidden_params)  # mutable-ok: downstream response metadata requires a mutable dict
+            if isinstance(_wrapper_hidden_params, dict)
+            else {}  # mutable-ok: downstream response metadata requires a mutable dict
         )
         # Store lightweight dict snapshots for stream_chunk_builder to reduce
         # repeated Pydantic attribute access in end-of-stream assembly.
diff --git a/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py b/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py
index 08112c2c04c..a538db85146 100644
--- a/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py
+++ b/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py
@@ -533,6 +533,10 @@ def test_extract_partial_responses_usage_real_bridge_iterator_pre_first_chunk():
             self.logging_obj = MagicMock()
             self._hidden_params = {"model_id": "deployment-123"}
 
+    class _FakeStreamWrapperWithoutHiddenParams:
+        def __init__(self) -> None:
+            self.logging_obj = MagicMock()
+
     iterator = LiteLLMCompletionStreamingIterator(
         model="anthropic/claude-3-5-sonnet-latest",
         litellm_custom_stream_wrapper=_FakeStreamWrapper(),
@@ -545,4 +549,12 @@ def test_extract_partial_responses_usage_real_bridge_iterator_pre_first_chunk():
     assert iterator._hidden_params == {"model_id": "deployment-123"}
     assert not iterator.collected_chat_completion_chunks
 
+    iterator_without_hidden_params = LiteLLMCompletionStreamingIterator(
+        model="anthropic/claude-3-5-sonnet-latest",
+        litellm_custom_stream_wrapper=_FakeStreamWrapperWithoutHiddenParams(),
+        request_input="hi",
+        responses_api_request={},
+    )
+
+    assert iterator_without_hidden_params._hidden_params == {}
     assert Router._extract_partial_responses_usage(iterator) is None