They won't likely announce it, you will just have to check here or on AT&Ts download site for the latest. Why wait for AT&T to release it? Just get the latest release that's out there and install it. 4.5.0.55 is the latest carrier release.
i do believe .77 has been out for a few weeks now.
i also have .69 on my 8310. only have one issue with it - when i do a battery pull the voice calls keep dropping until i do a memory clean, then the phone works perfectly.
last i heard .84 was to be the official TMobile release - perhaps ATT will follow suit