fix(vertex_ai): keep reasoning_effort unsupported on Vertex AI Mistral partner models

Vertex AI Mistral models reused MistralConfig, whose reasoning_effort
advertisement checks the mistral provider entry of the cost map, so
vertex_ai/mistral-medium-3 started advertising reasoning_effort and
drop_params stopped dropping it, turning a 200 into a Vertex 400.
VertexAIMistralConfig scopes that lookup to the vertex_ai provider, and
MistralConfig now reads the provider from its custom_llm_provider
property instead of a hardcoded "mistral".

litellm/__init__.py

@@ -1704,6 +1704,9 @@ if TYPE_CHECKING:
     from .llms.vertex_ai.vertex_ai_partner_models.ai21.transformation import (
         VertexAIAi21Config as VertexAIAi21Config,
     )
+    from .llms.vertex_ai.vertex_ai_partner_models.mistral.transformation import (
+        VertexAIMistralConfig as VertexAIMistralConfig,
+    )
     from .llms.bedrock.chat.invoke_handler import (
         AmazonCohereChatConfig as AmazonCohereChatConfig,
     )

litellm/_lazy_imports_registry.py

@@ -184,6 +184,7 @@ LLM_CONFIG_NAMES: Final = (
     "VertexAIAnthropicConfig",
     "VertexAILlama3Config",
     "VertexAIAi21Config",
+    "VertexAIMistralConfig",
     "AmazonCohereChatConfig",
     "AmazonBedrockGlobalConfig",
     "AmazonAI21Config",
@@ -771,6 +772,10 @@ _LLM_CONFIGS_IMPORT_MAP: Final = {
         ".llms.vertex_ai.vertex_ai_partner_models.ai21.transformation",
         "VertexAIAi21Config",
     ),
+    "VertexAIMistralConfig": (
+        ".llms.vertex_ai.vertex_ai_partner_models.mistral.transformation",
+        "VertexAIMistralConfig",
+    ),
     "AmazonCohereChatConfig": (
         ".llms.bedrock.chat.invoke_handler",
         "AmazonCohereChatConfig",

litellm/litellm_core_utils/get_supported_openai_params.py

@@ -190,7 +190,7 @@ def get_supported_openai_params(
     elif custom_llm_provider == "vertex_ai" or custom_llm_provider == "vertex_ai_beta":
         if request_type == "chat_completion":
             if model.startswith("mistral"):
-                return litellm.MistralConfig().get_supported_openai_params(model=model)
+                return litellm.VertexAIMistralConfig().get_supported_openai_params(model=model)
             elif model.startswith("codestral"):
                 return litellm.CodestralTextCompletionConfig().get_supported_openai_params(model=model)
             elif model.startswith("claude"):

litellm/llms/mistral/chat/transformation.py

@@ -35,14 +35,19 @@ if TYPE_CHECKING:
     import tiktoken
 
 
-def _accepted_reasoning_effort(model: str, requested: str) -> str:
-    declared: Final = declared_reasoning_efforts_for_model(model, "mistral")
+def _accepted_reasoning_effort(model: str, requested: str, custom_llm_provider: str) -> str:
+    declared: Final = declared_reasoning_efforts_for_model(model, custom_llm_provider)
     if declared is None:
         return requested
     accepted: Final = nearest_declared_reasoning_effort(requested, declared)
     if accepted != requested:
         verbose_logger.debug(
-            "mistral: %s takes reasoning_effort %s, sending %s in place of %s", model, declared, accepted, requested
+            "%s: %s takes reasoning_effort %s, sending %s in place of %s",
+            custom_llm_provider,
+            model,
+            declared,
+            accepted,
+            requested,
         )
     return accepted
 
@@ -103,9 +108,15 @@ class MistralConfig(OpenAIGPTConfig):
     def get_config(cls):
         return super().get_config()
 
+    @property
+    def custom_llm_provider(self) -> str:
+        return "mistral"
+
     def get_supported_openai_params(self, model: str) -> list[str]:
         is_magistral: Final = "magistral" in model.lower()
-        accepts_reasoning_effort: Final = is_magistral or supports_reasoning(model=model, custom_llm_provider="mistral")
+        accepts_reasoning_effort: Final = is_magistral or supports_reasoning(
+            model=model, custom_llm_provider=self.custom_llm_provider
+        )
         return [
             "stream",
             "temperature",
@@ -187,7 +198,7 @@ class MistralConfig(OpenAIGPTConfig):
             if param == "response_format":
                 optional_params["response_format"] = value
             if param == "reasoning_effort" and "magistral" not in model.lower():
-                optional_params["reasoning_effort"] = _accepted_reasoning_effort(model, value)
+                optional_params["reasoning_effort"] = _accepted_reasoning_effort(model, value, self.custom_llm_provider)
             if param in ("reasoning_effort", "thinking") and "magistral" in model.lower():
                 # Flag that we need to add reasoning system prompt
                 optional_params["_add_reasoning_prompt"] = True

litellm/llms/vertex_ai/vertex_ai_partner_models/mistral/transformation.py

@@ -0,0 +1,7 @@
+from litellm.llms.mistral.chat.transformation import MistralConfig
+
+
+class VertexAIMistralConfig(MistralConfig):
+    @property
+    def custom_llm_provider(self) -> str:
+        return "vertex_ai"

litellm/utils.py

@@ -4510,7 +4510,7 @@ def get_optional_params(
                     drop_params=bool(drop_params),
                 )
             else:
-                optional_params = litellm.MistralConfig().map_openai_params(
+                optional_params = litellm.VertexAIMistralConfig().map_openai_params(
                     model=model,
                     non_default_params=non_default_params,
                     optional_params=optional_params,
@@ -8380,7 +8380,7 @@ class ProviderConfigManager:
         elif model in litellm.vertex_mistral_models:
             if "codestral" in model:
                 return litellm.CodestralTextCompletionConfig()
-            return litellm.MistralConfig()
+            return litellm.VertexAIMistralConfig()
         elif model in litellm.vertex_ai_ai21_models:
             return litellm.VertexAIAi21Config()
         else:

tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/mistral/test_vertex_ai_partner_models_mistral_transformation.py

@@ -0,0 +1,17 @@
+import litellm
+
+
+def test_reasoning_effort_stays_unsupported_on_vertex_partner_models(local_model_cost_map):
+    assert "reasoning_effort" in litellm.get_supported_openai_params(
+        model="mistral-medium-3", custom_llm_provider="mistral"
+    )
+    assert "reasoning_effort" not in litellm.get_supported_openai_params(
+        model="mistral-medium-3", custom_llm_provider="vertex_ai"
+    )
+    dropped = litellm.get_optional_params(
+        model="mistral-medium-3",
+        custom_llm_provider="vertex_ai",
+        reasoning_effort="high",
+        drop_params=True,
+    )
+    assert "reasoning_effort" not in dropped