Registrations within off.ai, com.ai, net.ai, and org.ai are available unrestrictedly, worldwide, but don't appear to be getting much use. From September 15, 2009, second level registrations within .ai are available to everyone worldwide.
There is a $100 USD fee to become a registered user at whois.ai. Domains are $100 for each 2 year period. The order process is mainly manual and requires fax, and address verification, and a waiting period of 3 months after payment to "make sure there is no problem with your credit card".