Depends where you think humanity-on-Earth sits relative to the Culture. Since most of the Culture is human and we on Earth are as yet unaware of any spacefaring civilizations, I view it as a possible future for humanity. I would not be surprised if we encounter other life in space, but I'd be extremely startled if it turned out to be human life.

Pretty sure our present is post-Idiran-war based on the short story in The State Of The Art.

EDIT: I should specify that Contact is working on present-day Earth in that story, from what I recall.

Oh, you're right as an in-world thing. But I meant this sort of high technology described is in our future, ie I'm using 'in the future' as a proxy for 'science fiction.' Sorry about the confusion.

In cannon, Earth is an un-contacted planet and the Culture isn't our future. They are out there now.

Though, obviously, as a literary device you are right.

yes. And It makes a lot more sense if you're already familiar with the Culture, in which case the perspective of CP (from an avowed enemy of the Culture) is a lot more interesting. A prequel of sorts, but one I'd almost read last.