From 3c3081a502e74dae9c17f8317a8e54fc4fecac2f Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Wed, 4 Nov 2026 21:01:57 -0800
Subject: [PATCH] fix(mistral): leave tool_choice to the no-tools removal when
 no tools are sent

An unusable tool_choice on a request with no tools answered 400, while the
merge base and every other OpenAI-compatible route strip tool_choice from
such a request and answer 200. Map tool_choice only when tools are present.
---
 litellm/llms/mistral/chat/transformation.py     |  2 +-
 .../mistral/test_mistral_chat_transformation.py | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/litellm/llms/mistral/chat/transformation.py b/litellm/llms/mistral/chat/transformation.py
index ec2402e5f0b..61d237de2d8 100644
--- a/litellm/llms/mistral/chat/transformation.py
+++ b/litellm/llms/mistral/chat/transformation.py
@@ -282,7 +282,7 @@ class MistralConfig(OpenAIGPTConfig):
                 optional_params["tools"] = self._clean_tool_schema_for_mistral(value)
             if param == "stream" and value is True:
                 optional_params["stream"] = value
-            if param == "tool_choice":
+            if param == "tool_choice" and "tools" in non_default_params and non_default_params["tools"]:
                 match self._tool_choice_to_send(
                     model,
                     cast(object, value),  # cast-ok: untyped request params, the match narrows it
diff --git a/tests/unit/llms/mistral/test_mistral_chat_transformation.py b/tests/unit/llms/mistral/test_mistral_chat_transformation.py
index 8769ba655ac..42673e17acf 100644
--- a/tests/unit/llms/mistral/test_mistral_chat_transformation.py
+++ b/tests/unit/llms/mistral/test_mistral_chat_transformation.py
@@ -2084,14 +2084,17 @@ class TestMistralToolChoice:
     )
 
     def _request_body(
-        self, tool_choice: str | Mapping[str, object], drop_params: bool = False
+        self,
+        tool_choice: str | Mapping[str, object],
+        drop_params: bool = False,
+        tools: Sequence[ChatCompletionToolParam] | None = TOOLS,
     ) -> Mapping[str, object]:
         import litellm
 
         optional_params: Final = litellm.get_optional_params(
             model="mistral-large-latest",
             custom_llm_provider="mistral",
-            tools=list(self.TOOLS),
+            tools=None if tools is None else list(tools),
             tool_choice=tool_choice,
             drop_params=drop_params,
         )
@@ -2153,6 +2156,16 @@ class TestMistralToolChoice:
         with pytest.raises(litellm.UnsupportedParamsError, match="tool_choice"):
             self._request_body(tool_choice)
 
+    @pytest.mark.parametrize("tools", [None, ()])
+    @pytest.mark.parametrize("tool_choice", UNUSABLE_TOOL_CHOICES)
+    def test_unusable_tool_choice_without_tools_is_not_sent(
+        self,
+        local_model_cost_map: None,
+        tool_choice: str | Mapping[str, object],
+        tools: Sequence[ChatCompletionToolParam] | None,
+    ) -> None:
+        assert "tool_choice" not in self._request_body(tool_choice, tools=tools)
+
     @pytest.mark.parametrize("tool_choice", UNUSABLE_TOOL_CHOICES)
     def test_unusable_tool_choice_is_dropped_with_a_warning_under_drop_params(
         self, local_model_cost_map: None, tool_choice: str | Mapping[str, object], caplog: pytest.LogCaptureFixture