diff --git a/litellm/llms/anthropic/experimental_pass_through/responses_adapters/streaming_iterator.py b/litellm/llms/anthropic/experimental_pass_through/responses_adapters/streaming_iterator.py
index 461d254087d..4463732d265 100644
--- a/litellm/llms/anthropic/experimental_pass_through/responses_adapters/streaming_iterator.py
+++ b/litellm/llms/anthropic/experimental_pass_through/responses_adapters/streaming_iterator.py
@@ -86,8 +86,9 @@ class AnthropicResponsesStreamWrapper:
 
         # ---- message_start ----
         if event_type == "response.created":
-            self._sent_message_start = True
-            self._chunk_queue.append(self._make_message_start())
+            if not self._sent_message_start:
+                self._sent_message_start = True
+                self._chunk_queue.append(self._make_message_start())
             return
 
         # ---- content_block_start for a new output message item ----