Fix function_calling_llm support for custom models

- Add supports_function_calling() method to BaseLLM class with default True
- Add supports_function_calling parameter to LLM class to allow override of litellm check
- Add tests for both BaseLLM default and LLM override functionality
- Fixes #3708: Custom models not in litellm's list can now use function calling

Co-Authored-By: João <joao@crewai.com>

src/crewai/llm.py

@@ -299,6 +299,7 @@ class LLM(BaseLLM):
         callbacks: list[Any] | None = None,
         reasoning_effort: Literal["none", "low", "medium", "high"] | None = None,
         stream: bool = False,
+        supports_function_calling: bool | None = None,
         **kwargs,
     ):
         self.model = model
@@ -325,6 +326,7 @@ class LLM(BaseLLM):
         self.additional_params = kwargs
         self.is_anthropic = self._is_anthropic_model(model)
         self.stream = stream
+        self._supports_function_calling_override = supports_function_calling
 
         litellm.drop_params = True
 
@@ -1197,6 +1199,9 @@ class LLM(BaseLLM):
             )
 
     def supports_function_calling(self) -> bool:
+        if self._supports_function_calling_override is not None:
+            return self._supports_function_calling_override
+        
         try:
             provider = self._get_custom_llm_provider()
             return litellm.utils.supports_function_calling(

src/crewai/llms/base_llm.py

@@ -9,6 +9,7 @@ from typing import Any, Final
 
 DEFAULT_CONTEXT_WINDOW_SIZE: Final[int] = 4096
 DEFAULT_SUPPORTS_STOP_WORDS: Final[bool] = True
+DEFAULT_SUPPORTS_FUNCTION_CALLING: Final[bool] = True
 
 
 class BaseLLM(ABC):
@@ -82,6 +83,14 @@ class BaseLLM(ABC):
             RuntimeError: If the LLM request fails for other reasons.
         """
 
+    def supports_function_calling(self) -> bool:
+        """Check if the LLM supports function calling.
+
+        Returns:
+            True if the LLM supports function calling, False otherwise.
+        """
+        return DEFAULT_SUPPORTS_FUNCTION_CALLING
+
     def supports_stop_words(self) -> bool:
         """Check if the LLM supports stop words.
 

tests/test_custom_llm.py

@@ -358,3 +358,25 @@ def test_timeout_handling_llm():
     with pytest.raises(TimeoutError, match="LLM request failed after 2 attempts"):
         llm.call("Test message")
     assert len(llm.calls) == 2  # Initial call + failed retry attempt
+
+
+class MinimalCustomLLM(BaseLLM):
+    """Minimal custom LLM implementation that doesn't override supports_function_calling."""
+
+    def __init__(self):
+        super().__init__(model="minimal-model")
+
+    def call(
+        self,
+        messages: Union[str, List[Dict[str, str]]],
+        tools: Optional[List[dict]] = None,
+        callbacks: Optional[List[Any]] = None,
+        available_functions: Optional[Dict[str, Any]] = None,
+    ) -> Union[str, Any]:
+        return "Minimal response"
+
+
+def test_base_llm_supports_function_calling_default():
+    """Test that BaseLLM supports function calling by default."""
+    llm = MinimalCustomLLM()
+    assert llm.supports_function_calling() is True

tests/test_llm.py

@@ -711,3 +711,18 @@ def test_ollama_does_not_modify_when_last_is_user(ollama_llm):
     formatted = ollama_llm._format_messages_for_provider(original_messages)
 
     assert formatted == original_messages
+
+
+def test_supports_function_calling_with_override_true():
+    llm = LLM(model="custom-model/my-model", supports_function_calling=True)
+    assert llm.supports_function_calling() is True
+
+
+def test_supports_function_calling_with_override_false():
+    llm = LLM(model="gpt-4o-mini", supports_function_calling=False)
+    assert llm.supports_function_calling() is False
+
+
+def test_supports_function_calling_without_override():
+    llm = LLM(model="gpt-4o-mini")
+    assert llm.supports_function_calling() is True