It's apparently v3.5. That's what's available at https://chat.openai.com/auth/login. It's not clear to me how to access v4. They talk a lot about it but don't seem to provide any links to it.

As for posting information to get a summary, I haven't tried that, but what's the point of telling it the answer before asking it the question? Maybe I'm misunderstanding the use case here, but why would I need a machine to produce a summary of what I already know? My brain is usually pretty good at that on its own...