fix(anthropic): handle per-level reasoning_effort flags without supports_reasoning

litellm/router_utils/reasoning_effort_capability.py

@@ -148,16 +148,25 @@ def resolve_supported_reasoning_efforts(
     unset flag as () would let one custom deployment empty every level its mapped siblings agree
     on. deployment_is_mapped is that provenance, and an operator who wants either answer for an
     off-map deployment gets it by setting supports_reasoning explicitly.
+
+    If supports_reasoning is unset but at least one per-level flag (e.g.
+    supports_minimal_reasoning_effort) is present, treat it as implicitly True, since the
+    per-level flags are evidence the model supports reasoning. An explicit False always wins:
+    it is the operator's escape hatch and must not be overridden by inherited per-level flags.
     """
     supports_reasoning: Final = model_info.get("supports_reasoning")
-    if supports_reasoning is not True:
-        return () if supports_reasoning is False or deployment_is_mapped else None
+    if supports_reasoning is False:
+        return ()
+
+    flags: Final = _declared_effort_flags(model_info)
+    has_per_level_flag: Final = any(value is not None for value in flags.values())
+    if supports_reasoning is not True and not has_per_level_flag:
+        return () if deployment_is_mapped else None
 
     declared: Final = declared_reasoning_efforts(model_info)
     if declared is not None:
         return declared
 
-    flags: Final = _declared_effort_flags(model_info)
     if all(value is None for value in flags.values()):
         return None
 

tests/test_litellm/router_utils/test_reasoning_effort_capability.py

@@ -85,6 +85,25 @@ def test_opt_in_flag_set_false_stays_excluded(self):
         )
         assert resolved == ("none", "minimal", "low", "medium", "high")
 
+    def test_per_level_flag_without_supports_reasoning_treats_as_implicit_true(self):
+        resolved = resolve_supported_reasoning_efforts(
+            {
+                "supports_minimal_reasoning_effort": True,
+            },
+            deployment_is_mapped=True,
+        )
+        assert resolved == ("none", "minimal", "low", "medium", "high")
+
+    def test_explicit_supports_reasoning_false_wins_over_per_level_flags(self):
+        resolved = resolve_supported_reasoning_efforts(
+            {
+                "supports_reasoning": False,
+                "supports_minimal_reasoning_effort": True,
+            },
+            deployment_is_mapped=True,
+        )
+        assert resolved == ()
+
 
 class TestBareModelNameFallback:
     def test_a_prefixed_entry_inherits_the_flags_of_its_unprefixed_twin(self):