Never checked. But it does change once in a while. The router has a dyndns function which updates a DNS entry, but only for the router itself. But this is sufficient for the NAT port forwarding.
Let's say when your ipv6 prefix changes it is almost the same situation. Only that ipv4 bundles all traffic of all devices on one ip which obfuscates a bit.
But having the ipv6 prefix change you get a pile of problems (DNS, firewall), you don't have with ipv4.
The IPv6 prefix changes are disruptive, I agree. My prefix has been stable for a couple years, but on another ISP it would change every few months and was certainly annoying.
