Valve has announced that is making all of the Half-Life games available for free on Steam until the launch day of VR exclusive Half-Life: Alyx which is in March. This means Half-Life, Half-Life 2, Half-Life 2: Episode One, and Half-Life 2: Episode Two can be accessed with no charge. In addition, Valve is also making Half-Life: Opposing Force, Half-Life: Blue Shift, and Team Fortress Classic available for free during this promotion.
In the blog post Valve posted its reason for giving the games away for this time:
Half-Life: Alyx is set before the events of Half-Life 2 and the episodes, but the games share characters and story elements. The Half-Life: Alyx team believes that the best way to enjoy the new game is to play through the old ones, especially Half-Life 2 and the episodes, so we want to make that as easy as possible.
As the reasoning states, Half-Life: Alyx is set before Half-Life 2 and stars Alyx, one of the main characters of the series. The story revolves around Alyx and her father Eli starting the resistance against the occupying forces of the Combine. The game features exploration, puzzle-solving, and fighting the Combine forces. The game itself is built using the Source 2 engine. Half-Life: Alyx will be available on all PC VR headsets including Valve Index, Rift, Vive, and Window Mixed Reality. The game will be free to everyone who owns the Valve Index.