Marshall called the new policy a "unique solution to a frustrating situation," referring to the game being unable to keep servers perpetually busy despite "universally positive reviews."
"It's infuriating, but the important thing to do now is to make sure the people who have bought the game can enjoy it as intended," Marshall wrote. "The most frequent comment in my inbox at the moment is ‘this game is amazing, why aren't more people playing it?' Well, hopefully this move will bring in new interested players too, since they'll always be able to play friends when servers are quiet."
The promotion won't last forever, and keys are limited per player, Marshall added.
Last month, Marshall halved the game's price and included two copies with every purchase. Speaking with Polygon, he said the reduction was part of efforts to make it "less of a gamble for people" to try.