fix(anthropic): place strict flag at tool level, not inside input_schema

Anthropic enforces strict tool use only when `strict` is set at the tool
top level (sibling of name/input_schema). LiteLLM was placing it inside
input_schema where Anthropic silently ignores it, so callers thought
strict was engaged but the model emitted unconstrained tool arguments.

- Remove `strict` from AnthropicInputSchema (not part of the schema)
- Add `strict` to AnthropicMessagesTool (where Anthropic expects it)
- Extract strict from tool.function.strict (OpenAI canonical) or from
  parameters.strict (legacy), and set it on the tool object

Fixes #27490

litellm/llms/anthropic/chat/transformation.py

@@ -676,12 +676,17 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
                 **input_schema_filtered
             )
 
+            _strict = tool["function"].get("strict") or _input_schema.get("strict")
+
             _tool = AnthropicMessagesTool(
                 name=tool["function"]["name"],
                 input_schema=input_anthropic_schema,
                 type="custom",
             )
 
+            if _strict is True:
+                _tool["strict"] = True
+
             _description = tool["function"].get("description")
             if _description is not None:
                 _tool["description"] = _description

litellm/types/llms/anthropic.py

@@ -25,7 +25,6 @@ AnthropicInputSchema = TypedDict(
         "additionalProperties": Optional[bool],
         "required": Optional[List[str]],
         "$defs": Optional[Dict],
-        "strict": Optional[bool],
     },
     total=False,
 )
@@ -51,6 +50,7 @@ class AnthropicMessagesTool(TypedDict, total=False):
     defer_loading: bool
     allowed_callers: Optional[List[str]]
     input_examples: Optional[List[Dict[str, Any]]]
+    strict: bool
 
 
 class AnthropicComputerTool(TypedDict, total=False):

tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py

@@ -4703,3 +4703,99 @@ def test_sanitize_tool_names_in_request_no_tools_is_noop():
     forward, reverse = AnthropicConfig._sanitize_tool_names_in_request({"tools": []})
     assert forward == {}
     assert reverse == {}
+
+
+def test_map_tool_helper_strict_from_function_level():
+    """strict on tool.function (OpenAI canonical location) should be placed
+    at the tool top level, not inside input_schema."""
+    config = AnthropicConfig()
+
+    tool = {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get weather",
+            "strict": True,
+            "parameters": {
+                "type": "object",
+                "properties": {"city": {"type": "string"}},
+                "required": ["city"],
+                "additionalProperties": False,
+            },
+        },
+    }
+
+    result, _ = config._map_tool_helper(tool)
+    assert result is not None
+    assert result.get("strict") is True
+    assert "strict" not in result["input_schema"]
+
+
+def test_map_tool_helper_strict_from_parameters():
+    """strict inside tool.function.parameters (legacy placement) should be
+    moved to the tool top level."""
+    config = AnthropicConfig()
+
+    tool = {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get weather",
+            "parameters": {
+                "type": "object",
+                "properties": {"city": {"type": "string"}},
+                "required": ["city"],
+                "additionalProperties": False,
+                "strict": True,
+            },
+        },
+    }
+
+    result, _ = config._map_tool_helper(tool)
+    assert result is not None
+    assert result.get("strict") is True
+    assert "strict" not in result["input_schema"]
+
+
+def test_map_tool_helper_no_strict_omits_field():
+    """When strict is not set, it should not appear on the tool."""
+    config = AnthropicConfig()
+
+    tool = {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get weather",
+            "parameters": {
+                "type": "object",
+                "properties": {"city": {"type": "string"}},
+            },
+        },
+    }
+
+    result, _ = config._map_tool_helper(tool)
+    assert result is not None
+    assert "strict" not in result
+    assert "strict" not in result["input_schema"]
+
+
+def test_map_tool_helper_strict_false_omits_field():
+    """strict=False should not be forwarded to Anthropic."""
+    config = AnthropicConfig()
+
+    tool = {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get weather",
+            "strict": False,
+            "parameters": {
+                "type": "object",
+                "properties": {"city": {"type": "string"}},
+            },
+        },
+    }
+
+    result, _ = config._map_tool_helper(tool)
+    assert result is not None
+    assert "strict" not in result