Update 3: Eurogamer has spoken with a Microsoft spokesperson whom confirmed they currently have no plans to release any Halo titles on Steam.
Update 2: Valve has removed a large number of the Game Hubs we processed earlier today.
Update: Valve has removed the ""Halo 3"" Game Hub, and it now redirects to the Steam Store.
Actually, no. Not by any stretch of the imagination is it confirmed.
Since a few hours ago, we have started processing Steam Hub names in the database (hence why a ton of apps were "updated"). Some people noticed things such as Halo 3 appearing in the database. Now, these Game Hub pages might very well be real/truthful, since I have no idea how they are made. Does Valve make these, or are they automatically made when a publisher enters/reserves a game?
In both cases, there are lots of errors in the Steam Database, some bigger than others, and this might just be one of them. Is it a placeholder and is Halo 3 actually on it's way to Steam? Or is it just another Steam Hub page that one of the publishers made for name-reserveration's sake? Or did some completely different developer need a cover to put a test version of his/her game under? Who knows?!
Everything you read on this site is subject to change, and until there's an official announcement from whomever is making whatever, it's not 100% truth. For all we know, at one point all the Halo's might have been coming to Steam, until they decided to go XBOX exclusive with Halo 3. We know just as much as you do.
For now, let's just take the Game Hub information with a
pinch ton of salt.