note 5 IPv6 supported (on at&t)

This note 5 is the first phone I have with AT&T that's getting a non-local (2600::380::....) IPv6 address from the cell tower. I wasn't getting ipv6 on my nexus 6 last week (same LTE network.)

Does anyone know if this was something that AT&T recently enabled, or if they are only doing router announcements to specific APN's and/or h/w?