diff --git a/litellm/router.py b/litellm/router.py
index 7267f6eb3ba..1c658f9ef3a 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -3072,7 +3072,9 @@ class Router:
         # Native path: completed_response is set only if RESPONSE_COMPLETED
         # arrived before the error (uncommon mid-stream but worth checking).
         # Already ResponseAPIUsage-shaped — return as-is.
-        completed: Final = source_iterator.completed_response
+        # Use getattr because a bridge iterator whose __init__ never ran
+        # may not have the attribute at all (#38511).
+        completed: Final = getattr(source_iterator, "completed_response", None)
         if isinstance(
             completed,
             (ResponseCompletedEvent, ResponseFailedEvent, ResponseIncompleteEvent),
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 5370089eef5..1587c416c70 100644
--- a/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py
+++ b/tests/router_unit_tests/test_router_aresponses_streaming_fallback.py
@@ -116,6 +116,33 @@ def test_extract_partial_responses_usage_bridge_iterator_no_completed_response()
     assert Router._extract_partial_responses_usage(iterator) is None
 
 
+def test_extract_partial_responses_usage_no_completed_response_attr():
+    """
+    Regression for #38511: the native fallback path must not crash with
+    AttributeError when the source iterator lacks a ``completed_response``
+    attribute entirely. The original error handler read
+    ``source_iterator.completed_response`` as a bare attribute access, which
+    masks the real streaming error with an AttributeError. Using getattr
+    lets the original exception propagate intact.
+    """
+    from litellm.responses.litellm_completion_transformation.streaming_iterator import (
+        LiteLLMCompletionStreamingIterator,
+    )
+
+    class _NoCompletedResponseBridge(LiteLLMCompletionStreamingIterator):
+        """A bridge iterator whose __init__ never ran, leaving no
+        ``completed_response`` attribute — the scenario that triggers #38511.
+        """
+
+        def __init__(self) -> None:
+            self.collected_chat_completion_chunks: list = []
+
+    iterator = _NoCompletedResponseBridge()
+    assert not hasattr(iterator, "completed_response")
+    usage = Router._extract_partial_responses_usage(iterator)
+    assert usage is None
+
+
 # -------- _combine_responses_fallback_usage --------