Fix LiteAgent isinstance checks to accept BaseLLM instances

- Fix setup_llm method to check isinstance(self.llm, BaseLLM) instead of LLM
- Fix ensure_guardrail_is_callable method to check isinstance(self.llm, BaseLLM)
- Add comprehensive test for CustomLLM with guardrails functionality
- Resolves issue #3112 where CustomLLM classes couldn't use guardrails

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

src/crewai/lite_agent.py

@@ -41,6 +41,7 @@ from crewai.agents.parser import (
 )
 from crewai.flow.flow_trackable import FlowTrackable
 from crewai.llm import LLM
+from crewai.llms.base_llm import BaseLLM
 from crewai.tools.base_tool import BaseTool
 from crewai.tools.structured_tool import CrewStructuredTool
 from crewai.utilities import I18N
@@ -209,7 +210,7 @@ class LiteAgent(FlowTrackable, BaseModel):
     def setup_llm(self):
         """Set up the LLM and other components after initialization."""
         self.llm = create_llm(self.llm)
-        if not isinstance(self.llm, LLM):
+        if not isinstance(self.llm, BaseLLM):
             raise ValueError("Unable to create LLM instance")
 
         # Initialize callbacks
@@ -232,7 +233,7 @@ class LiteAgent(FlowTrackable, BaseModel):
         elif isinstance(self.guardrail, str):
             from crewai.tasks.llm_guardrail import LLMGuardrail
 
-            assert isinstance(self.llm, LLM)
+            assert isinstance(self.llm, BaseLLM)
 
             self._guardrail = LLMGuardrail(description=self.guardrail, llm=self.llm)
 

tests/test_lite_agent.py

@@ -418,3 +418,55 @@ def test_agent_output_when_guardrail_returns_base_model():
     result = agent.kickoff(messages="Top 10 best players in the world?")
 
     assert result.pydantic == Player(name="Lionel Messi", country="Argentina")
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_lite_agent_with_custom_llm_and_guardrails():
+    """Test that CustomLLM (inheriting from BaseLLM) works with guardrails."""
+    from crewai.llms.base_llm import BaseLLM
+    
+    class CustomLLM(BaseLLM):
+        def __init__(self, response="Custom response"):
+            super().__init__(model="custom-model")
+            self.response = response
+            self.call_count = 0
+
+        def call(self, messages, tools=None, callbacks=None, available_functions=None, from_task=None, from_agent=None):
+            self.call_count += 1
+            if isinstance(messages, str):
+                messages = [{"role": "user", "content": messages}]
+            for message in messages:
+                if isinstance(message["content"], str):
+                    message["content"] = [{"type": "text", "text": message["content"]}]
+            return self.response
+
+    custom_llm = CustomLLM(response="Brazilian soccer players are the best!")
+    
+    agent = Agent(
+        role="Sports Analyst",
+        goal="Analyze soccer players",
+        backstory="You analyze soccer players and their performance.",
+        llm=custom_llm,
+        guardrail="Only include Brazilian players"
+    )
+    
+    result = agent.kickoff("Tell me about the best soccer players")
+    
+    assert custom_llm.call_count > 0
+    assert "Brazilian" in result.raw
+    
+    custom_llm2 = CustomLLM(response="Original response")
+    
+    def test_guardrail(output):
+        return (True, "Modified by guardrail")
+    
+    agent2 = Agent(
+        role="Test Agent",
+        goal="Test goal",
+        backstory="Test backstory",
+        llm=custom_llm2,
+        guardrail=test_guardrail
+    )
+    
+    result2 = agent2.kickoff("Test message")
+    assert result2.raw == "Modified by guardrail"