SteamDB notes the inclusion of a file called hl3.txt in the latest Dota 2 update (thanks VG247). This contains snippets of code, while the name of the file naturally inspires speculation that Valve is either hinting at something, or they've just taken to trolling us about their shooter series. On a somewhat related note, a thread from a couple of weeks ago on reddit recalls Valve's 2006 announcement that Half-Life 2: Episode One was gold (thanks Ant). Since this press release called Ep1 "the first in a trilogy of episodes that will conclude by Christmas of 2007," the thread takes that as the official announcement of Episode Three. They note this makes the seemingly forgotten continuation of the shooter series the new king of Valve Time, as it has surpassed the 3,417 day gap between the announcement and release of Team Fortress 2. Coincidentally, Episode Two was released on October 10, 2007, so it's almost exactly eight years since the series stalled.