Valve Software's popular online team-based shooter Team Fortress 2 is going free to play - a first for a Valve Software title. Valve plans to support the title on virtual items.. like hats. All current owners of the PC game will automatically become premium account holders. Premium members get access to rare and cosmetic items through random item drops, the ability to store more items in your backpack, and more powerful trading and crafting abilities
The gameplay experience (beyond the extra baubles TF2 premium account holders get) will be the same for everyone. Gamers who purchase any item from Team Fortress 2's digital storefront (Mann Co. Store) will also be granted premium account privileges. Players spend real money to buy virtual items such as weapons for various character classes, and a wide variety of hats. Those who bought Team Fortress 2 will also receive a "Proof of Purchase hat" for any character.
You can learn more about the changes here.