diff --git a/src/crewai/llm.py b/src/crewai/llm.py
index d62694f14..47295303b 100644
--- a/src/crewai/llm.py
+++ b/src/crewai/llm.py
@@ -119,7 +119,16 @@ def suppress_warnings():
 class LLM:
     def __init__(
         self,
-        model: str,
+        model: Union[str, 'BaseLanguageModel'],
+        """Initialize LLM instance.
+        
+        Args:
+            model: The model identifier; should not start with 'models/'.
+                  Examples: 'gemini/gemini-1.5-pro', 'anthropic/claude-3'
+            
+        Raises:
+            ValueError: If the model name starts with 'models/'.
+        """
         timeout: Optional[Union[float, int]] = None,
         temperature: Optional[float] = None,
         top_p: Optional[float] = None,
@@ -142,10 +151,13 @@ class LLM:
         reasoning_effort: Optional[Literal["none", "low", "medium", "high"]] = None,
         **kwargs,
     ):
+        # Constants for model name validation
+        INVALID_MODEL_PREFIX = "models/"
+        
         # Validate model name
-        if isinstance(model, str) and model.startswith('models/'):
+        if isinstance(model, str) and model.startswith(INVALID_MODEL_PREFIX):
             raise ValueError(
-                'Model name should not start with "models/". '
+                f'Invalid model name "{model}": Model names should not start with "{INVALID_MODEL_PREFIX}". '
                 'Use the provider prefix instead (e.g., "gemini/model-name").'
             )
         
diff --git a/tests/llm_test.py b/tests/llm_test.py
index 876e98e0e..44d8d6a52 100644
--- a/tests/llm_test.py
+++ b/tests/llm_test.py
@@ -252,15 +252,27 @@ def test_validate_call_params_no_response_format():
     llm._validate_call_params()
 
 
-def test_model_name_validation():
-    """Test that model names with 'models/' prefix are rejected."""
-    with pytest.raises(ValueError, match="should not start with \"models/\""):
-        LLM(model="models/gemini/gemini-1.5-pro")
+class TestModelNameValidation:
+    """Tests for model name validation in LLM class."""
+    
+    def test_models_prefix_rejection(self):
+        """Test that model names with 'models/' prefix are rejected."""
+        with pytest.raises(ValueError, match="should not start with \"models/\""):
+            LLM(model="models/gemini/gemini-1.5-pro")
 
-    # Valid model names should work
-    LLM(model="gemini/gemini-1.5-pro")
-    LLM(model="anthropic/claude-3-opus-20240229-v1:0")
-    LLM(model="openai/gpt-4")
+    def test_valid_model_names(self):
+        """Test that valid model names are accepted."""
+        LLM(model="gemini/gemini-1.5-pro")
+        LLM(model="anthropic/claude-3-opus-20240229-v1:0")
+        LLM(model="openai/gpt-4")
+        LLM(model="openai/gpt-4 turbo")  # Space in model name should work
+        
+    def test_edge_cases(self):
+        """Test edge cases for model name validation."""
+        with pytest.raises(ValueError):
+            LLM(model="")  # Empty string
+        with pytest.raises(TypeError):
+            LLM(model=None)  # None value
 
 
 @pytest.mark.vcr(filter_headers=["authorization"])