Portal 2 has sold over 4 million units worldwide, Valve has confirmed.
So revealed Valve's David Sawyer in an interview with Neogamr about the new map editor DLC released today.
"The Puzzle Maker lets people try their hand at creating puzzles while also letting them discover, share, and easily play what they and other Portal 2 players are coming up with," he later said.
"So the editor needed to let anyone pick it up and not just use it, but enjoy the process of using it. We think people will have fun with the Puzzle Maker even if they never share their work with anyone else."
The site says that Valve chose not to adress questioning over the possible release of the map editor on the Xbox or PS3 versions of Portal 2.
The DLC, titled the 'Perpetual Testing Initiative', was released today for free to anyone with a PC copy of Portal 2.