The current registrars for ".ai" are below and growing fast:

1. 101domain.com
2. instra.com
3. marcaria.com
4. nameaction.com
5. idcicp.com
6. quyu.net
7. markmonitor.com
8. 1api.net
9. ai-domain.com
10. zhuce.ai
11. EPAG Domainservices GmbH
12. EU Technology(HK) Limited
13. Domain Club
14. bNamed.net
15. Tool Domains
16. Nameshield
17. 007Names
18. Netz0
19. zenaida.cate.ai
20. porkbun.com
21. namecheap.com
    
    To be on this list a registrar just has to handle ".ai" registrations, renewals, and transfers (in and out).