Ancient Go should now be compatible with the new version of OGS, fixing online play.
The only noticeable change is that the authentication process. OGS removed the application specific authentication code so from now on logging in will use your regular OGS username and password.
Ancient Go does not store your password, but you wont have to log in every time as OGS is able to use the authorization for a good period.
It might be a good idea to play unranked, shorter games for a while just in case there are any issues I missed. In my testing everything is functional but there might still be edge cases etc.