Fix Deepseek-v3-250324 empty responses issue (#2657)

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

src/crewai/llm.py

@@ -91,6 +91,7 @@ LLM_CONTEXT_WINDOW_SIZES = {
     "gemini-1.5-flash-8b": 1048576,
     # deepseek
     "deepseek-chat": 128000,
+    "deepseek-v3-250324": 128000,
     # groq
     "gemma2-9b-it": 8192,
     "gemma-7b-it": 8192,
@@ -930,6 +931,17 @@ class LLM(BaseLLM):
                 )  # Create a copy to avoid modifying the original
                 messages.append({"role": "user", "content": "Please continue."})
             return messages
+            
+        # Handle Deepseek-v3-250324 model - it also requires the last message to have a role of 'user'
+        if "deepseek-v3-250324" in self.model.lower():
+            # Check if the last message has a role of 'assistant'
+            if messages and messages[-1]["role"] == "assistant":
+                # Add a dummy user message to ensure the last message has a role of 'user'
+                messages = (
+                    messages.copy()
+                )  # Create a copy to avoid modifying the original
+                messages.append({"role": "user", "content": "Please continue."})
+            return messages
 
         # Handle Anthropic models
         if not self.is_anthropic:

tests/llm_test.py

@@ -407,6 +407,37 @@ def test_anthropic_message_formatting(anthropic_llm, system_message, user_messag
     assert formatted[0] == system_message
 
 
+@pytest.fixture
+def deepseek_llm():
+    """Fixture for Deepseek-v3-250324 LLM instance."""
+    return LLM(model="deepseek-v3-250324")
+
+
+def test_deepseek_message_formatting(deepseek_llm):
+    """Test Deepseek-v3-250324 message formatting."""
+    # Test when last message is assistant
+    messages = [
+        {"role": "user", "content": "Hello"},
+        {"role": "assistant", "content": "Hi there"},
+    ]
+    formatted = deepseek_llm._format_messages_for_provider(messages)
+    assert len(formatted) == 3
+    assert formatted[0]["role"] == "user"
+    assert formatted[1]["role"] == "assistant"
+    assert formatted[2]["role"] == "user"
+    assert formatted[2]["content"] == "Please continue."
+
+    # Test when last message is not assistant
+    messages = [
+        {"role": "assistant", "content": "Hi there"},
+        {"role": "user", "content": "Hello"},
+    ]
+    formatted = deepseek_llm._format_messages_for_provider(messages)
+    assert len(formatted) == 2
+    assert formatted[0]["role"] == "assistant"
+    assert formatted[1]["role"] == "user"
+
+
 def test_deepseek_r1_with_open_router():
     if not os.getenv("OPEN_ROUTER_API_KEY"):
         pytest.skip("OPEN_ROUTER_API_KEY not set; skipping test.")