Valve is going to tell us about this VR Half-Life: Alyx on November 21 at 10 am Pacific Time. The announcement was made on Valve's relatively new Twitter account and this was the first tweet on it. This could've come across as suspicious but the account is verified and some of the people from Valve retweeted it, therefore it's safe to say that this is a valid announcement.
The original Half-Life was released on November 19, 1998, and Half-Life 2 was launched on November 16, 2004, so it’s been a long wait for the game’s fans. It seems that November is Half-Life’s month.