Source: Half-Life Fallout

Half-Life Fallout reports the news that the Blog that revealed the now official release date long before Valve did (Gotten via a Source), now reports that the same Source revealed something that could indicate that Valve is planning to release something for Half-Life 2 around the release of the game. And the words indicate that it could be a Multi Player for the game:

However, here's something I thought that you would want to know. The same source who scored on the game going gold sent this to me last night:
There's going to be a special treat near launch or soon after for those who are upset that Counter-Strike Source is the only multiplayer offered out of the box. I'd hate to ruin the surprise but let's just say traditionalists will be happy even if it's just one map at first. Physics Cannon!

Do note, nothing official, it's all a rumor at the moment and only time will tell if it's a hoax or not.