The StarCraft II Arcade along with all its features are now available to all StarCraft II: Starter Edition players for free. That means all custom games, maps and mods can be played for free with the StarCraft II: Starter Edition.
In addition, today’s StarCraft II Patch 2.1 has unlocked all three races for Starter Edition players. Mod developers can now create Extension Mods that can be applied to any melee map from the Custom Games list. Numerous other changes in StarCraft II Patch 2.1 include a level cap increase from 30 to 35 for each race, clan and group improvements and balance changes to each race.
You can view more detailed patch notes at the source link below.