fix(mistral): never round reasoning_effort none onto the strength ladder

litellm/router_utils/reasoning_effort_capability.py

@@ -103,15 +103,17 @@ def declared_reasoning_efforts_for_model(model: str, custom_llm_provider: str) -
     return declared_reasoning_efforts(entry)
 
 
-REASONING_EFFORT_STRENGTH_ORDER: Final = ("none", "minimal", "low", "medium", "high", "xhigh", "max")
+REASONING_EFFORT_STRENGTH_ORDER: Final = ("minimal", "low", "medium", "high", "xhigh", "max")
 _STRENGTH_RANK: Final = MappingProxyType({effort: rank for rank, effort in enumerate(REASONING_EFFORT_STRENGTH_ORDER)})
 
 
 def nearest_declared_reasoning_effort(requested: str, declared: Sequence[str]) -> str:
     """Rounds a request up to the weakest declared level at least as strong as it, and down to the
     strongest declared level when it asks for more than the model has, so the caller gets no less
-    reasoning than it asked for instead of a rejected call. A level outside the strength order is
-    returned as is for upstream to judge."""
+    reasoning than it asked for instead of a rejected call. none is the off switch rather than a
+    strength, so it is never rounded onto the ladder and no level is rounded down to it: a caller
+    who turned reasoning off must not be billed for it, and a model that cannot turn it off says so
+    itself. A level outside the strength order is likewise returned as is for upstream to judge."""
     ranked: Final = sorted(
         (effort for effort in declared if effort in _STRENGTH_RANK), key=lambda effort: _STRENGTH_RANK[effort]
     )

tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py

@@ -99,7 +99,8 @@ class TestMistralReasoningSupport:
             ("mistral-medium-latest", "xhigh", "high"),
             ("mistral-small-latest", "medium", "high"),
             ("mistral-vibe-cli-latest", "medium", "high"),
-            ("zai-glm-5", "none", "low"),
+            ("zai-glm-5", "none", "none"),
+            ("zai-glm-5", "minimal", "low"),
             ("zai-glm-5", "medium", "high"),
             ("zai-glm-5", "xhigh", "max"),
             ("zai-glm-5-2", "medium", "medium"),

tests/test_litellm/router_utils/test_reasoning_effort_capability.py

@@ -425,9 +425,13 @@ class TestNearestDeclaredReasoningEffort:
 
     def test_an_undeclared_level_rounds_up_to_the_next_declared_one(self):
         assert nearest_declared_reasoning_effort("medium", ("none", "high")) == "high"
-        assert nearest_declared_reasoning_effort("none", ("low", "high", "max")) == "low"
+        assert nearest_declared_reasoning_effort("minimal", ("low", "high", "max")) == "low"
         assert nearest_declared_reasoning_effort("xhigh", ("low", "high", "max")) == "max"
 
+    def test_none_is_a_switch_that_is_never_rounded_in_either_direction(self):
+        assert nearest_declared_reasoning_effort("none", ("low", "high", "max")) == "none"
+        assert nearest_declared_reasoning_effort("medium", ("none",)) == "medium"
+
     def test_a_level_above_the_ceiling_takes_the_strongest_declared_one(self):
         assert nearest_declared_reasoning_effort("max", ("none", "high")) == "high"
         assert nearest_declared_reasoning_effort("xhigh", ("none", "low", "medium", "high")) == "high"