The information about the Linux port has been published on the CDR database
Altitude, a multiplayer action game developed and published by Nimbly Games, will be arriving on Steam for Linux, soon.Altitude is a 2D action game, in which the player controls a plane and fights in huge multiplayer battles, against friends or other online users.
The game comes with a few multiplayer modes, including Free For All, Team Deathmatch, Demolition, and 1-life Deathmatch. Players can also cooperate with other players and join The Altitude ProLeague, a competitive tournament scene.
The information about the Linux version is taken from the CDR database and by no means is it completely certain. The CDR Database is a record of data that describes every Steam game and subscription provided by Valve for the Steam service.
Usually, the new entries in the Steam database are first visible in the CDR Database before their official launch.