Soon Valve will release an update that adds three new weapons and achievements for the Soldier and Demoman classes in Team Fortress 2. Until the day it goes live, though, Valve's staging a competition between the two classes.
"A secret, exclusive seventh weapon has also been developed by the TF2 team," Valve's Robin Walker explains on the TF2 blog. "In other words, either the Soldier or the Demo (but NOT both) is walking out of this update with one more weapon than the other. If you want your class to have it, you're going to have to fight for it.
"The more Demomen you kill as the Soldier class will help ensure the Soldier gets the weapon at the end of the week. The more Soldiers you kill as the Demo will help the Demo class get the exclusive seventh weapon."
You can check the status of the competition every day at a new War Update page. That's also where they'll be releasing new information about the update's contents over the course of the week.
