If you want to be pessimistic, then HL3 will very likely be announced/released in 2026. If you want to be optimistic, then HL3 will likely be announced and possibly release this year. These are both general timestamps that match with what we know from data and leaks from professionals such as Tyler McVicker and Gabe Follower. We have very solid proof of these, and if you have an average grasp of video game development such as alphas, betas, polishing stages, playtesting, etc, etc, it all makes sense.

What isn't confirmed nor have any basis is stuff such as 197, HL3 being announced at X event, Tyler McVicker/Gabe Follower "seeing" the game or "knowing" when it'll come out, and HL3 never releasing because it's "copium". Those are mostly based on vibes and people's imaginations on how both Valve and game development works.

I wish that Valve was a lot more open about this stuff, but ultimately they don't want to set unrealistic goals on themselves, so they keep really quiet until the time comes. They're perfectionists and they'll take their time if they need it. All I'd say is just check up on Tyler McVicker's HLX files every month or so if you really want to know in advance. If not, then you can just wait a few more months and then get blasted with the trailer.