It's not too often games are treated with significant DLC installments a year or two after its launch; the game usually has grabbed the attention of the core audience, or it's begun to decline in terms of popularity. If we rarely see that, then, we almost never see games receive DLC, expansions at that, ten years after its launch, but that's exactly what Square-Enix is planning to do with Final Fantasy XI.
According to the company, the upcoming ten-year anniversary expansion, dubbed "Seekers of Adoulin," will pit players in two new locations, the Ulbuka Continent and the Sacred City of Adoulin, and will feature two new job classes, the Geomancers and Rune Fencers. The new locations will feature entirely new enemies and gameplay mechanics for players to master, along with new, secret "power spots" to be found throughout the world.
Seekers of Adoulin is set to be released to the public in 2013 for Xbox 360 and PC, and will be the fifth major expansion for Final Fantasy XI. We'll keep you up to date on further details pertaining to the DLC as they become available.
Source: [Square Enix press release]