OpenAI has done the reasonable thing of not exposing the probability distribution per generated token so it's very hard to use that to completely map to their models. Ultimately, you still do need a very large base model to compete.
can you elaborate on what that means?
Their newer chat style endpoint for the GPT-3.5-turbo and GPT-4 models no longer supports this. https://platform.openai.com/docs/api-reference/chat