The content pack is available as a free download for players of all access levels, and the highlight of the pack is the third and final chapter in the Fortress of Solitude raid series. GU6 is titled The Deadly Double Cross, in large part due to the betrayal of General Zod and the precarious position inside the Fortress of Solitude Sunstone Matrix that players will find themselves in as a result.
Raid encounters aren't the only thing new in the update, though, and GU6 adds plenty of new gear (including Kryptonian military weapons forged from the Sunstone crystals). Head to the official website for more game details, and don't forget the patch note discussion on the official forums.
[Source: SOE press release]