Could you point me to where they claim to have fine-tuned Codex?
From what I can see they claim:
> We use OpenAI’s davinci-codex engine for all of our generations. We fix all of Codex’s hyperparameters to be the same for all experiments: top-p which is the portion p of the token probability mass a language model samples from at each step is set to 1, sampling temperature is set to 0 (i.e. argmax), and response length is set to 200 tokens.
BTW - OpenAI Davinci costs $0.06 per 1000 tokens. Codex is currently free in closed beta, but I guess cost will be the same. I would be happy to pay even 100x ($6) for correct solutions to advanced mathematical problems. The issue is that this paper has ridiculous evaluation and Codex does not work anywhere near as good as they claim. It is pure hype by people who do not appear to be affiliated with OpenAI.