Rumour has it that Valve plans to announce a new Half-Life game, and soon. Apparently based around protagonist Alyx Vance, the game may see a release as early as Q1 2020. It looks set to be sad news for those holding out for Half-Life 3 or even just Half-Life 2: Episode 3, though.
https://www.notebookcheck.net/New-Half-Life-game-details-leaked-ahead-of-The-Game-Awards.443188.0.html