Blizzard announced that StarCraft 2 will become free-to-play at November 14th.
Players who get StarCraft 2 for free will get access to Wings of Liberty campaign, and the cooperative mode and competitive multiplayer. If you already own Wings of Liberty, you’ll get free access to Heart of the Swarm instead.
But, free player’s co-op commander capped at level 5. And have to achieve 10 First Wins of the Day to join ranked multiplayer matches.