Betting it was Claude. That's the only LLM that will stand up to me!
"Claude" is a big program that wraps a coding agent around a specific model. It would be the specific model that "stands up to you". I post this pedantry only because it may be helpful to you to realize this for other reasons.
In fact it was Gemini, but I don't remember which version and there are big differences. I'm signed up for all the betas and I switch among them frequently.