[Bug Fix] grok-4 does not support the stop param (#12646)

* bug fix - using stop reason with grok 4

* fixes for XAI stop params

* test_xai_grok_4_stop_not_supported

* test_xai_grok_4_stop_not_supported

litellm/llms/xai/chat/transformation.py

@@ -50,7 +50,7 @@ class XAIChatConfig(OpenAIGPTConfig):
             "web_search_options",
         ]
         # for some reason, grok-3-mini does not support stop tokens
-        if "grok-3-mini" not in model:
+        if self._supports_stop_reason(model):
             base_openai_params.append("stop")
         try:
             if litellm.supports_reasoning(
@@ -61,6 +61,13 @@ class XAIChatConfig(OpenAIGPTConfig):
             verbose_logger.debug(f"Error checking if model supports reasoning: {e}")
 
         return base_openai_params
+    
+    def _supports_stop_reason(self, model: str) -> bool:
+        if "grok-3-mini" in model:
+            return False
+        elif "grok-4" in model:
+            return False
+        return True
 
     def map_openai_params(
         self,

tests/llm_translation/test_xai.py

@@ -118,6 +118,21 @@ def test_xai_check_for_stop_in_supported_params():
     assert "stop" not in supported_params
 
 
+@pytest.mark.parametrize("model", ["xai/grok-4", "xai/grok-4-0709"])
+def test_xai_grok_4_stop_not_supported(model):
+    """
+    Test that grok-4 models do not support the stop parameter
+
+    Issue: https://github.com/BerriAI/litellm/issues/12635
+    """
+    supported_params = XAIChatConfig().get_supported_openai_params(
+        model=model
+    )
+    assert "stop" not in supported_params
+
+
+
+
 @pytest.mark.parametrize("stream", [False, True])
 def test_completion_xai(stream):
     try:
@@ -130,9 +145,9 @@ def test_completion_xai(stream):
             },
         ]
         response = completion(
-            model="xai/grok-3-mini-beta",
+            model="xai/grok-4",
             messages=messages,
-            stream=stream,
+            stream=stream
         )
         print(response)