Gabe Newell is a mythic entity in the game industry. He usually pretty quiet in his dealings, and as one of the keepers of Half Life 3, that only builds up the persona.
Well, I reckon Newell is in store for a ton of questions about just that game as the Valve man is set for a reddit AMA today. If you did want to see what he has to say, just head over to reddit at 6pm ET/3pm PST.
My guess is he won't answer anything about Half Life 3 directly, but there could be a tease here or there about the fate of that production. It's possible, even likely though, that he will mute the game's title. I'll report back with any juicy tidbits.