diff --git a/litellm/proxy/common_request_processing.py b/litellm/proxy/common_request_processing.py
index 3fca267e321..69c2cb3f0f0 100644
--- a/litellm/proxy/common_request_processing.py
+++ b/litellm/proxy/common_request_processing.py
@@ -3045,10 +3045,17 @@ class ProxyBaseLLMRequestProcessing:
 
         Raw async generators from passthrough routes bypass all three and
         would orphan the closure, so they are not armed here.
+
+        The router wraps iterators that cannot carry _hidden_params in
+        HiddenParamsAsyncIteratorWrapper, so class sniffing runs on the
+        unwrapped inner iterator.
         """
         from litellm.litellm_core_utils.streaming_handler import CustomStreamWrapper
+        from litellm.router_utils.add_retry_fallback_headers import HiddenParamsAsyncIteratorWrapper
 
-        if isinstance(response, CustomStreamWrapper):
+        unwrapped: Final = response._inner if isinstance(response, HiddenParamsAsyncIteratorWrapper) else response
+
+        if isinstance(unwrapped, CustomStreamWrapper):
             # Intentionally a live reference (not a copy) — mirrors
             # ProxyLogging.post_call_success_hook which also mutates
             # data["guardrail_to_apply"] during iteration.
@@ -3075,7 +3082,7 @@ class ProxyBaseLLMRequestProcessing:
             LiteLLMCompletionStreamingIterator,
         )
 
-        if isinstance(response, LiteLLMCompletionStreamingIterator):
+        if isinstance(unwrapped, LiteLLMCompletionStreamingIterator):
             _captured_bridge_logging_obj: Final = logging_obj
 
             async def _on_deferred_bridged_stream_complete(assembled_response: object, cache_hit: object) -> None:
diff --git a/tests/test_litellm/proxy/guardrails/test_deferred_guardrail_logging.py b/tests/test_litellm/proxy/guardrails/test_deferred_guardrail_logging.py
index 99fae277bdd..8fde4cc9d5e 100644
--- a/tests/test_litellm/proxy/guardrails/test_deferred_guardrail_logging.py
+++ b/tests/test_litellm/proxy/guardrails/test_deferred_guardrail_logging.py
@@ -1352,6 +1352,40 @@ class TestArmDeferredStreamDispatch:
         assert recorded["cache_hit"] is False
         assert recorded["prefer_async_handlers"] is True
 
+    @pytest.mark.asyncio
+    async def test_router_wrapped_bridged_iterator_gets_csw_arg_shape(self):
+        """The router wraps iterators without _hidden_params in
+        HiddenParamsAsyncIteratorWrapper before the proxy arms deferral, so
+        every production streamed /v1/responses reaches arming wrapped;
+        sniffing the wrapper instead of the inner iterator armed the 1-arg
+        native closure against the CSW's 2-arg stored shape and leaked a
+        TypeError 500 frame into the stream."""
+        from litellm.responses.litellm_completion_transformation.streaming_iterator import (
+            LiteLLMCompletionStreamingIterator,
+        )
+        from litellm.router_utils.add_retry_fallback_headers import (
+            HiddenParamsAsyncIteratorWrapper,
+        )
+
+        logging_obj, recorded = self._dispatch_recording_logging_obj()
+        wrapped = HiddenParamsAsyncIteratorWrapper(object.__new__(LiteLLMCompletionStreamingIterator))
+
+        self._processor()._arm_deferred_stream_dispatch(
+            response=wrapped,
+            route_type="aresponses",
+            user_api_key_dict=MagicMock(),
+            logging_obj=logging_obj,
+        )
+
+        assembled = object()
+        logging_obj._deferred_stream_complete_args = (assembled, False)
+        ProxyLogging._fire_deferred_stream_logging({"litellm_logging_obj": logging_obj})
+        await asyncio.sleep(0)
+
+        assert recorded["result"] is assembled
+        assert recorded["cache_hit"] is False
+        assert recorded["prefer_async_handlers"] is True
+
     @pytest.mark.asyncio
     async def test_native_stream_closure_enqueues_single_coroutine(self):
         from litellm.litellm_core_utils.logging_worker import GLOBAL_LOGGING_WORKER