We've known about the existence of the Omega DLC for Mass Effect 3 since the retirement of the Doctors from their position at BioWare, but we haven't really heard anything officially about it. Truth be told, what I'm about to report isn't exactly an official announcement either, but it appears like some info about the DLC was given by producer Mike Gamble at Comic-Con, although the video from which it was extracted is now private.
Thankfully, Eurogamer has the rundown, which includes a release date, a price tag and an assessment of the DLC's scope:
The single-player campaign expansion launches for PC, PlayStation 3 and Xbox 360 on 27th November for 1200 Microsoft Points or $15 (about £10). European PlayStation players will likely see it on the 28th.
Omega will be "double the size" of the largest Mass Effect 3 DLC so far, Mass Effect 3 producer Mike Gamble explained at New York Comic-Con. (In terms of actual game content Gamble is likely referring to this summer's Leviathan DLC. In terms of file size the largest is the 2GB Extended Cut, although that is the Xbox 360 DLC file limit).
Omega will also be the most expensive Mass Effect 3 DLC so far (or of the entire series, if you don't count Mass Effect 2's 1200 Point Cerberus Network pass which came free with new copies).
The expansion will see players team up with ousted Omega ruler Aria T'loak to retake the station from Cerberus control.