This page on the Team Fortress 2 Website has details on CP_STEEL, a community map planned as part of the upcoming Team Fortress 2 Heavy update. This kicks off a week-long roll-out of new info on the class, as outlined in this schedule, which promises new information every weekday through next Tuesday. Here's the deal on the new map:

A complex Attack/Defense control point map, with some unique gameplay. Unlike most TF2 maps, capturing a control point modifies the layout of the map, opening and closing routes for each team. As a result, the offensive team has a wide variety of tactical choices around how they'd like to assault the final point. Should they use Scouts and Soldiers to rush the final point with only the routes they start with? Should they go for the side control points and open up more routes to the final? Should they capture extra points to shut down the defender's routes? The many choices keep the map interesting for a long time, providing a wide variety of experiences in a game.