The Internet Archive is not, in fact, completely online (as the article explains but the title doesn’t). The Wayback Machine, which is part of it, is kind of online but (in my experience) you are going to experience HTTP 504 timeouts from time to time on the first query for a given (URL, date) pair as it seemingly goes out to slower storage. (Long delays happened in the past occasionally as well but not to the point of a 504.)