Valve: ‘Secret’ Team Fortress 2 project coming this year

Work on Team Fortress 2 continues to push ahead at full Steam (see what I did there?), with Valve promising new “secret” content this year.
The whole “secret” thing means (by definition) that we have no idea what it is, but we know what it’s not:
“…it isn’t a hat, it isn’t a map… but it’s really cool,” reads a blog post on the official Team Fortress blog. 
That’s all well and good, but where are the new details regarding the future of the Half Life? That’s it, from now on every news story regarding Valve will contain a jibe at the lack of Half Life info.
Source: Team Fortress