The official exhibitor list for Gamescom 2018 revealed that Valve will be present at this major gaming event. And before someone says it, no; the team will not announce or reveal Half-Life 3. So temper your expectations, especially you that thought that this would be THAT big moment, otherwise you will be disappointed.
Our guess is that Valve will showcase its card game that has been under development for a while, Artifact. However, the team may also showcase In the Valley of Gods.
Back in April 2018, Valve acquired Campo Santo. Campo Santo was responsible for Firewatch and is currently working on In the Valley of Gods, which is now listed as a Valve game.
So yeah, while Valve will not reveal a new main game in the Half-Life universe, it will unquestionably showcase at least one game. There was also a report that Valve was working on some VR games but that report was back in 2017 and we haven’t heard anything about them since then.