Information about the Linux version has been published in the CDR database
Portal, an innovative single-player game developed and published by Valve, will soon arrive on Steam for Linux.Portal was first released back in 2007, along with Half-Life 2 and Team Fortress 2. Little did Valve know that Portal would become one of their most successful titles.
According to Valve, the game is designed to change the way players approach, manipulate, and surmise the possibilities in a given environment.
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.