diff --git a/litellm/llms/anthropic/experimental_pass_through/adapters/handler.py b/litellm/llms/anthropic/experimental_pass_through/adapters/handler.py
index 897ca3bf893..f4de468092d 100644
--- a/litellm/llms/anthropic/experimental_pass_through/adapters/handler.py
+++ b/litellm/llms/anthropic/experimental_pass_through/adapters/handler.py
@@ -181,7 +181,10 @@ class LiteLLMMessagesToCompletionTransformationHandler:
                 "include_usage": True,
             }
 
-        excluded_keys = {"anthropic_messages"}
+        excluded_keys = {
+            "anthropic_messages",
+            "output_config",
+        }
         extra_kwargs = extra_kwargs or {}
         for key, value in extra_kwargs.items():
             if (
diff --git a/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_experimental_pass_through_messages_handler.py b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_experimental_pass_through_messages_handler.py
index 33628e1d19d..ed90038f372 100644
--- a/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_experimental_pass_through_messages_handler.py
+++ b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_experimental_pass_through_messages_handler.py
@@ -64,6 +64,31 @@ def test_anthropic_experimental_pass_through_messages_handler_dynamic_api_key_an
         assert mock_completion.call_args.kwargs["custom_key"] == "custom_value"
 
 
+def test_anthropic_messages_adapter_drops_output_config_for_azure():
+    """
+    Test that output_config is not forwarded to litellm.completion for Azure models.
+    """
+    from litellm.llms.anthropic.experimental_pass_through.messages.handler import (
+        anthropic_messages_handler,
+    )
+
+    with patch("litellm.completion", return_value=MagicMock()) as mock_completion:
+        try:
+            anthropic_messages_handler(
+                max_tokens=100,
+                messages=[{"role": "user", "content": "Hello, how are you?"}],
+                model="azure/o1",
+                api_key="test-api-key",
+                output_config={"effort": "medium"},
+            )
+        except (ValueError, TypeError, AttributeError) as e:
+            print(f"Error: {e}")
+
+        mock_completion.assert_called_once()
+        call_kwargs = mock_completion.call_args.kwargs
+        assert "output_config" not in call_kwargs
+
+
 def test_anthropic_experimental_pass_through_messages_handler_custom_llm_provider():
     """
     Test that litellm.completion is called when a custom LLM provider is given