It appears that Team Fortress 2 may be adding more to the game than we realised in the recent updates. Various hints spanning from 2010 to 2012 point to a new mode which will be including a new addition of robots.
"Mann vs. Machine" was most recently suggested by a suspicious splatter mark appearing this week on the logo of Team Fortress' website. The splatter mark links to the image below, which you can click to enlarge. The image is of a birth certificate which indicates the brothers who founded the opposing RED and BLU teams had a third sibling named Gray, who was "absconded with" soon after birth.
Previous hidden assets on the Team Fortress 2 website and within the game's code have pointed to robotic variants of each of the game's nine distinct classes, which you can see in the gallery below. When this update will hit, IF it will hit, is unclear. But it seems to us that a big update is coming soon.