Brand director Karl Stewart said the content, which was announced as a timed exclusive to Xbox 360 at E3, will not feel like content missing from the main game.
"We had the opportunity to sort of say we're doing something unique [at Microsoft's press conference] and something more," Stewart said.
"As I said, it's a timed piece of content. It's still early in the process for us, we haven't fleshed out the full stories and what we're going to do.
"What we're saying is you will be able to play the game from start to finish, and the DLC will not feel like it's a chunk of the game taken out. It will be unique to what's happening after the story."
Stewart continued: "I think it's important to show people that we're actively looking at how to expand. In this day and age people have an expectation and an expectation of playing DLC is one, so for us there's tons of mystery on the island, which - even in a ten-plus hour game - it's going to be hard to answer everything.