Apart from just when the game will be in our eager hands (or live on our systems), whether or not multiplayer will be included in Half-Life 2 has been one of the biggest questions about the game. While Valve has so far implied that Half-Life 2's multiplayer mode is simply Counter-Strike: Source, nothing specific or official had been announced.
However, Halflife2.net today posted an interview with PC Gamer's Chuck Osborn, who happens to be among the first to review the final game. And there, in the interview, Osborn gives us an answer: "Counter-Strike Source is the multiplayer." No separate deathmatch. Just CS: Source.
News source: ign.com