You can ask chatGPT about arxiv.org papers if you have the doi and the full title if the paper is from 2021 or earlier

This renders the extension pretty useless for older papers, doesn't it? There doesn't seem to be a fallback to prompt older papers in a whole because it exceeds the prompt limit.

Well yes in a way, the extension settings include the prompt they're using, so you can formulate your own prompt along the same lines.

I think the extension is only useful for someone who spends a lot of time doing research on arxiv.org, (and if the quality of the summary is good enough, the jury's still out on that one)

bing.com/new doesn’t have a length restriction, and the Edge sidebar version can do it like this.

Disclosure: I work at MSFT but not on Bing

It must have some length restriction though, no? A GPT always has a max context window if I understand correctly. It's likely Bing has access to models with a much larger context window than what is accessibly through the OpenAI API.