Cautious Hooray: Half-Life 3 is being actively developed? Let the rumors start, yet again.
https://www.neogaf.com/forum/showthread.php?t=688711
and
https://www.rockpapershotgun.com/2013/10/02/cautious-hooray-half-life-3-being-actively-developed/
and Valve registers European trademark for Half-Life 3
https://arstechnica.com/gaming/2013/10/valve-registers-european-trademark-for-half-life-3/