According to an update to The Walking Dead spotted on Steam's database, Telltale Games' Game of the Year is getting DLC titled 400 Days. Underneath the entries for The Walking Dead on PC and Mac is an encrypted "Walking Dead 400 Days DLC" component, which is also mentioned in the section history on the database.
Over the past week, Telltale Games has posted short clips on their Vine teasing new content for The Walking Dead. They display official documents and photos of three characters, including one of a man named Vince, a Woman named Bonnie, a man named Russel, and hinting at the number 400.
In February, The Walking Dead writer Gary Whitta mentioned that fans "won't have to wait for season two to play more Walking Dead" and that "There may very well be more Walking Dead from Telltale before season two." Looks like I know what to expect from my meeting with Telltale Games at E3 now.