The updates for IPv6 with ARC was included in the last production release:
Firstly and at long last, we’re releasing IPv6 network compatibility for ARC. This change should allow many users stranded by their internet service provider’s adaptation of the IPv6 address format to use ARC outside of their home WiFi. Please note that, much like port forwarding in the previous release of ARC, the expanded compatibility will function best on simple networks with standard configurations, and certain ISPs or router setups may still require additional steps or workarounds.