http://6pb473duz5o6kdvedrvplpyce33ezwjxkehbwtagytxe6yqal4xe44yd.onion/articles/xmpp.html
It says they will delete or anonymize IP addresses after 7 days, and that IP addresses will only be retained beyond 7 days under certain circumstances. The circumstances are vague, but can be assumed to be in the event of say, an attack on their server, or something of the sort.