The original StarCraft along with the Brood War expansion pack is available for free on Blizzard’s official website.
For the StarCraft Remastered, we’d still have to wait. Although, a new patch v1.18 is out now; this brings a few enhancements for the game like Observer mode, replay autosave, fixes and general improvements.
Blizzard announced making the original StarCraft free around the same time as the Remastered, but this decision was implemented alongside the 1.18 patch. While the original game was released back in 1998, the remastered version has kept the basic spirit of the game alive, which includes all the original game play.
You can check the complete patch notes here.
For more updates, stay tuned.