GPT-4 support (langchain-ai#1778)

langchain/llms/openai.py

@@ -163,7 +163,8 @@ class BaseOpenAI(BaseLLM, BaseModel):
 
     def __new__(cls, **data: Any) -> Union[OpenAIChat, BaseOpenAI]:  # type: ignore
         """Initialize the OpenAI object."""
-        if data.get("model_name", "").startswith("gpt-3.5-turbo"):
+        model_name = data.get("model_name", "")
+        if model_name.startswith("gpt-3.5-turbo") or model_name.startswith("gpt-4"):
             return OpenAIChat(**data)
         return super().__new__(cls)