Valve founder Gabe Newell's Reddit AMA was derailed today, but you can tune in to watch the hive mind pester the Steam boss tomorrow.
As promised, Newell opened a thread in the AMA subreddit earlier today. Unfortunately, he did not submit his AMA through Reddit's approved channel, and also failed to abide by its guidelines of not posting until at most half an hour before scheduled start time.
As a result, moderators closed the thread down. An hour after the AMA was due to start, a new thread had not been opened, and Reddit moderators confirmed they had been unable to reach Newell through contacts at Valve.