If you mean Subliming, it is not tied to "perfect AI" or anything like that in the books. It is not actually clear what the prerequisite from it is, but the books have examples of races Subliming that are less technologically proficient than the Culture (notably, the Chelgrians).
Nor does it imply that Sublimed civilizations are somehow more of an utopia. They are clearly more capable, but in terms of social organization, again, Chelgrians are a strong counter-example where the Sublimed part of the race literally demands the rest of it to commit genocide as a form of revenge to get access to heaven.
Nor does it imply that Sublimed civilizations are somehow more of an utopia. They are clearly more capable, but in terms of social organization, again, Chelgrians are a strong counter-example where the Sublimed part of the race literally demands the rest of it to commit genocide as a form of revenge to get access to heaven.