fix(openai): validate logprobs/top_p against reasoning_effort for gpt-5.1/5.2

logprobs, top_p, top_logprobs are only accepted by OpenAI when
reasoning_effort="none". Add validation matching the existing
temperature logic: raise UnsupportedParamsError or drop when
reasoning_effort is set to other values.

litellm/llms/openai/chat/gpt_5_transformation.py

@@ -124,6 +124,24 @@ class OpenAIGPT5Config(OpenAIGPTConfig):
                 "max_tokens"
             )
 
+        # gpt-5.1/5.2 support logprobs, top_p, top_logprobs only when reasoning_effort="none"
+        if self.is_model_gpt_5_1_model(model):
+            sampling_params = ["logprobs", "top_logprobs", "top_p"]
+            has_sampling = any(p in non_default_params for p in sampling_params)
+            if has_sampling and reasoning_effort not in (None, "none"):
+                if litellm.drop_params or drop_params:
+                    for p in sampling_params:
+                        non_default_params.pop(p, None)
+                else:
+                    raise litellm.utils.UnsupportedParamsError(
+                        message=(
+                            "gpt-5.1/5.2 only support logprobs, top_p, top_logprobs when "
+                            "reasoning_effort='none'. Current reasoning_effort='{}'. "
+                            "To drop unsupported params set `litellm.drop_params = True`"
+                        ).format(reasoning_effort),
+                        status_code=400,
+                    )
+
         if "temperature" in non_default_params:
             temperature_value: Optional[float] = non_default_params.pop("temperature")
             if temperature_value is not None:

tests/test_litellm/llms/openai/test_gpt5_transformation.py

@@ -473,3 +473,39 @@ def test_gpt5_1_top_p_passthrough(config: OpenAIConfig):
         drop_params=False,
     )
     assert params["top_p"] == 0.9
+
+
+def test_gpt5_1_logprobs_rejected_with_reasoning_effort(config: OpenAIConfig):
+    """logprobs/top_p/top_logprobs are rejected when reasoning_effort != 'none'."""
+    for effort in ["low", "medium", "high"]:
+        with pytest.raises(litellm.utils.UnsupportedParamsError):
+            config.map_openai_params(
+                non_default_params={"logprobs": True, "reasoning_effort": effort},
+                optional_params={},
+                model="gpt-5.1",
+                drop_params=False,
+            )
+
+
+def test_gpt5_1_top_p_rejected_with_reasoning_effort(config: OpenAIConfig):
+    """top_p is rejected when reasoning_effort != 'none'."""
+    with pytest.raises(litellm.utils.UnsupportedParamsError):
+        config.map_openai_params(
+            non_default_params={"top_p": 0.9, "reasoning_effort": "high"},
+            optional_params={},
+            model="gpt-5.1",
+            drop_params=False,
+        )
+
+
+def test_gpt5_1_logprobs_dropped_with_reasoning_effort(config: OpenAIConfig):
+    """logprobs/top_p are dropped when reasoning_effort != 'none' and drop_params=True."""
+    params = config.map_openai_params(
+        non_default_params={"logprobs": True, "top_p": 0.9, "reasoning_effort": "high"},
+        optional_params={},
+        model="gpt-5.1",
+        drop_params=True,
+    )
+    assert "logprobs" not in params
+    assert "top_p" not in params
+    assert params["reasoning_effort"] == "high"