A news story
posted in Bluesnews.com
indicated that several new developments were on their way for HL2 from Steam. They would be correcting a "sound stuttering bug" which was the result of texture thrashing on your video card or AGP memory. They also promised to release the Source SDK. And, they also promised a surprise.
That surprise turns out to be... drum roll... Half Life 2 deathmatch
! The Steam forum had this
post on the subject, along with a teaser image.