There's a mysterious new, undocumented model in the https://chat.lmsys.org/ arena chat tool called "gpt2-chatbot" - you can access it by selecting "Direct Chat" and then picking it from the big select menu there
It's providing responses that feel significantly more impressive than GPT-4, for both factual-knowledge lookup and logic puzzles. It's possible this is a stealth preview launch of something like GPT-4.5
