Until LangChain adds support for a ChatOpenAI cache, here is a drop-in class that adds support for it

cached_chat_open_ai.py

# PoC to cache prompts. Drop in your code. 
# Andreas 'blackhc' Kirsch, 2023

from typing import List, Optional

import langchain
from langchain import OpenAI
from langchain.cache import SQLiteCache
from langchain.schema import (
    AIMessage,
    BaseMessage,
    ChatGeneration,
    ChatResult,
    Generation
)


langchain.llm_cache = SQLiteCache(".chat.langchain.db")


class CachedChatOpenAI(ChatOpenAI):
    def _generate(self, messages: List[BaseMessage], *args, **kwargs) -> ChatResult:
        # NOTE: the cache does currently not respect additional arguments beyond the messages.
        messages_prompt = repr(messages)
        if langchain.llm_cache:
            results = langchain.llm_cache.lookup(messages_prompt, self.model_name)
            if results:
                assert len(results) == 1
                result: Generation = results[0]
                chat_result = ChatResult(
                    generations=[ChatGeneration(message=AIMessage(content=result.text))],
                    llm_output=result.generation_info)
                return chat_result
        chat_result = super()._generate(messages, *args, **kwargs)
        if langchain.llm_cache:
            assert len(chat_result.generations) == 1
            result = Generation(
                text=chat_result.generations[0].message.content,
                generation_info=chat_result.llm_output
            )
            langchain.llm_cache.update(messages_prompt, self.model_name, [result])
        return chat_result


chat_model = CachedChatOpenAI(max_tokens=512, model_kwargs=dict(temperature=0.))

from typing import List, Optional
from langchain.schema import (
    AIMessage,
    BaseMessage,
    ChatGeneration,
    ChatResult,
    Generation
)

Thanks! Updated 🤗

For v0.0.154 version, you should add:

    run_manager: Optional[CallbackManagerForLLMRun] = None,

cause of https://github.com/hwchase17/langchain/blob/258c3198559da5844be3f78680f42b2930e5b64b/langchain/chat_models/openai.py#L270

Thanks! I've replaced additional arguments with *args, **kwargs now. However, the cache does not respect stop etc so beware relying on that 🙏