After a reveal, Valve confirmed that all of the major Half-Life games and add-ons are now available for free on Steam as part of a pre-Alyx promotion. They'll be free to play - not free to own - for the next two months, or up until the release of Half-Life: Alyx, which is still on track for a March release.
This free to play offer extends to Half-Life, Half-Life 2 and its supporting episodes, and major additions like Half-Life: Opposing Force, Half-Life 1: Source, and Half-Life: Blue Shift. However, Half-Life 2: Deathmatch is still $4.99.
Jump over and enjoy some Half-life