GPTBot ignoring robots.txt and hammering single URL in a loop — potential infinite crawl bug

It’s entirely plausible that someone is pretending to be GPTBot. Have you checked the IP Address(es) attached to the requests?

You can match it here, and in the future ensure that any user agent as GPTBOT is valid

https://openai.com/gptbot.json

Lastly, you could be more explicit and include this in your robots.txt (not sure if this would help)

User-agent: GPTBot
Disallow: /*?*nocache=*