Stable is apparently rolling out as we speak So wait till you get the update notification If all goes well and they don't halt the rollout you should get the ota soon
Just an fyi the newest update was a beta release,some people who got the ota for a12 were new batch beta testers it seems and there's a new ota for those on a11 So stable will likely releases somewhere further down this month (their official schedule states dec as stable release date too)