It was 2005, but yes

little fun story is, that I was part of a small mod team back then. And by pure chance we were in contact with someone at valve, who told us about the plans of opening up steam to 3rd party games and mods. And our mod was considered to be put as one of the first games to be put into the store. at least for a short time (alas, didn’t work out for… internal reasons. I think mainly because it was a mod and not a full game)