Got ninja'ed but here's the relevant copy: https://starcraft2.com/en-us
On November 14, 2017, large parts of StarCraft II's single-player and multiplayer modes will become accessible for free (See Below). It’s never been a better time to begin your StarCraft II story. Wings of Liberty Campaign
The award-winning StarCraft II: Wings of Liberty story campaign is free in its entirety. Versus Mode
Access Unranked and Versus AI for free; unlock Ranked with 10 first wins of the day in Unranked or Versus AI. Commanders up to Level 5
Kerrigan, Raynor, and Artanis are completely free, and all other Commanders are free up to level 5.