Team Fortress 2 is threatened by an alien menace in the latest special event.
TF2: Invasion was created by and for community members over the past year. Launching today, it adds four new maps.
The month long event runs through November 5. If you want to participate, grab an Invasion Community Update Pass from the Mann Co. Store and activate the included Invasion Community Update Coin. Your kills will be counted towards a game-wide total, with coin stats locked at the end of the event. All proceeds from sales of the pass will go to the community development team.
During the event, exclusive Invasion crates will drop, containing rare items, weapons and effects. You need an Invasion Community Update Key to open these crates. It sounds like these are sold separately, because proceeds from sales of the keys will be shared with Valve.
Visit the Invasion hub for more details, or just watch the trailer below.