Remove none support from reasoning param

litellm/llms/azure/chat/gpt_5_transformation.py

@@ -2,6 +2,8 @@
 
 from typing import List
 
+import litellm
+from litellm.exceptions import UnsupportedParamsError
 from litellm.llms.openai.chat.gpt_5_transformation import OpenAIGPT5Config
 from litellm.types.llms.openai import AllMessageValues
 
@@ -33,7 +35,34 @@ class AzureOpenAIGPT5Config(AzureOpenAIConfig, OpenAIGPT5Config):
         drop_params: bool,
         api_version: str = "",
     ) -> dict:
-        return OpenAIGPT5Config.map_openai_params(
+        reasoning_effort_value = (
+            non_default_params.get("reasoning_effort")
+            or optional_params.get("reasoning_effort")
+        )
+
+        if reasoning_effort_value == "none":
+            if litellm.drop_params is True or (
+                drop_params is not None and drop_params is True
+            ):
+                non_default_params = non_default_params.copy()
+                optional_params = optional_params.copy()
+                if non_default_params.get("reasoning_effort") == "none":
+                    non_default_params.pop("reasoning_effort")
+                if optional_params.get("reasoning_effort") == "none":
+                    optional_params.pop("reasoning_effort")
+            else:
+                raise UnsupportedParamsError(
+                    status_code=400,
+                    message=(
+                        "Azure OpenAI does not support reasoning_effort='none'. "
+                        "Supported values are: 'low', 'medium', and 'high'. "
+                        "To drop this parameter, set `litellm.drop_params=True` or for proxy:\n\n"
+                        "`litellm_settings:\n drop_params: true`\n"
+                        "Issue: https://github.com/BerriAI/litellm/issues/16704"
+                    ),
+                )
+
+        result = OpenAIGPT5Config.map_openai_params(
             self,
             non_default_params=non_default_params,
             optional_params=optional_params,
@@ -41,6 +70,11 @@ class AzureOpenAIGPT5Config(AzureOpenAIConfig, OpenAIGPT5Config):
             drop_params=drop_params,
         )
 
+        if result.get("reasoning_effort") == "none":
+            result.pop("reasoning_effort")
+
+        return result
+
     def transform_request(
         self,
         model: str,

tests/test_litellm/llms/azure/chat/test_azure_gpt5_transformation.py

@@ -104,7 +104,12 @@ def test_azure_gpt5_codex_series_transform_request(config: AzureOpenAIGPT5Config
 
 # GPT-5.1 temperature handling tests for Azure
 def test_azure_gpt5_1_temperature_with_reasoning_effort_none(config: AzureOpenAIGPT5Config):
-    """Test that Azure GPT-5.1 supports any temperature when reasoning_effort='none'."""
+    """Test that Azure GPT-5.1 supports any temperature when reasoning_effort='none'.
+    
+    Note: Azure OpenAI doesn't support reasoning_effort='none', so it's dropped from the params.
+    However, the temperature logic still works correctly because the parent treats missing
+    reasoning_effort the same as 'none' for gpt-5.1.
+    """
     params = config.map_openai_params(
         non_default_params={"temperature": 0.5, "reasoning_effort": "none"},
         optional_params={},
@@ -113,7 +118,8 @@ def test_azure_gpt5_1_temperature_with_reasoning_effort_none(config: AzureOpenAI
         api_version="2024-05-01-preview",
     )
     assert params["temperature"] == 0.5
-    assert params["reasoning_effort"] == "none"
+    # Azure doesn't support reasoning_effort="none", so it should be dropped
+    assert "reasoning_effort" not in params or params.get("reasoning_effort") != "none"
 
 
 def test_azure_gpt5_1_temperature_without_reasoning_effort(config: AzureOpenAIGPT5Config):