fix(azure): drop tool_choice without tools

DEVX-829

litellm/llms/azure/chat/gpt_transformation.py

@@ -280,10 +280,17 @@ class AzureOpenAIConfig(BaseConfig):
         ordered_messages: Final = system_messages_first(messages) if litellm.openai_system_messages_first else messages
         stripped_messages: Final = drop_tool_reference_parts_from_tool_messages(ordered_messages)
         azure_messages: Final = convert_to_azure_openai_messages(hoist_images_from_tool_messages(stripped_messages))
+        request_params: Final = {
+            key: value
+            for key, value in optional_params.items()
+            if key != "tool_choice"
+            or optional_params.get("tools")
+            or optional_params.get("functions")
+        }
         return {
             "model": model,
             "messages": azure_messages,
-            **optional_params,
+            **request_params,
             **sanitized_tools_update(optional_params),
         }
 

tests/test_litellm/llms/azure/chat/test_azure_chat_gpt_transformation.py

@@ -333,3 +333,126 @@ class TestAzureToolSchemaCombinatorFlattening:
         )
         assert "tools" not in request
         assert request["temperature"] == 0.2
+
+
+@pytest.mark.parametrize("tool_choice", ["none", "auto"])
+def test_azure_drops_tool_choice_without_tools_or_functions(tool_choice: str) -> None:
+    optional_params = {"tool_choice": tool_choice, "temperature": 0.2}
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params=optional_params,
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert "tool_choice" not in request
+    assert request["temperature"] == 0.2
+    assert optional_params["tool_choice"] == tool_choice
+
+
+def test_azure_tools_empty_drops_tool_choice() -> None:
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"tools": [], "tool_choice": "auto"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["tools"] == []
+    assert "tool_choice" not in request
+
+
+def test_azure_functions_empty_drops_tool_choice() -> None:
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"functions": [], "tool_choice": "none"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["functions"] == []
+    assert "tool_choice" not in request
+
+
+def test_azure_preserves_tool_choice_with_tools() -> None:
+    tools = [{"type": "function", "function": {"name": "get_weather", "parameters": {}}}]
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"tools": tools, "tool_choice": "auto"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["tools"] == tools
+    assert request["tool_choice"] == "auto"
+
+
+def test_azure_preserves_tool_choice_with_legacy_functions() -> None:
+    functions = [{"name": "get_weather", "parameters": {}}]
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"functions": functions, "tool_choice": "auto"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["functions"] == functions
+    assert request["tool_choice"] == "auto"
+
+
+def test_azure_preserves_function_call_without_tools() -> None:
+    request = AzureOpenAIConfig().transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"function_call": "none", "tool_choice": "auto"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["function_call"] == "none"
+    assert "tool_choice" not in request
+
+
+def test_azure_gpt5_drops_tool_choice_without_tools() -> None:
+    request = AzureOpenAIGPT5Config().transform_request(
+        model="gpt5_series/gpt-5.6-sol",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"tool_choice": "none"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["model"] == "gpt-5.6-sol"
+    assert "tool_choice" not in request
+
+
+@pytest.mark.asyncio
+async def test_azure_async_transform_drops_tool_choice_without_tools() -> None:
+    request = await AzureOpenAIConfig().async_transform_request(
+        model="gpt-4o",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"tool_choice": "none"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert "tool_choice" not in request
+
+
+@pytest.mark.asyncio
+async def test_azure_gpt5_async_transform_drops_tool_choice_without_tools() -> None:
+    request = await AzureOpenAIGPT5Config().async_transform_request(
+        model="gpt5_series/gpt-5.6-sol",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={"tool_choice": "auto"},
+        litellm_params={"custom_llm_provider": "azure"},
+        headers={},
+    )
+
+    assert request["model"] == "gpt-5.6-sol"
+    assert "tool_choice" not in request

tests/test_litellm/llms/azure/chat/test_azure_chat_o_series_transformation.py

@@ -14,7 +14,7 @@ async def test_azure_chat_o_series_transformation():
     provider_config = AzureOpenAIO1Config()
     model = "o_series/web-interface-o1-mini"
     messages = [{"role": "user", "content": "Hello, how are you?"}]
-    optional_params = {}
+    optional_params = {"tool_choice": "none"}
     litellm_params = {}
     headers = {}
 
@@ -23,6 +23,7 @@ async def test_azure_chat_o_series_transformation():
     )
     print(response)
     assert response["model"] == "web-interface-o1-mini"
+    assert "tool_choice" not in response
 
 
 def test_azure_o_series_transform_request_flattens_top_level_anyof():