count tokens for new OpenAI model versions

Author: kylrth

langchain/chat_models/openai.py

@@ -466,12 +466,12 @@ def get_num_tokens_from_messages(self, messages: List[BaseMessage]) -> int:
         if sys.version_info[1] <= 7:
             return super().get_num_tokens_from_messages(messages)
         model, encoding = self._get_encoding_model()
-        if model == "gpt-3.5-turbo-0301":
+        if model.startswith("gpt-3.5-turbo"):
             # every message follows <im_start>{role/name}\n{content}<im_end>\n
             tokens_per_message = 4
             # if there's a name, the role is omitted
             tokens_per_name = -1
-        elif model == "gpt-4-0314":
+        elif model.startswith("gpt-4"):
             tokens_per_message = 3
             tokens_per_name = 1
         else: