Dota 2 released through Steam in July 2013.
Valve launched the game after nearly two years of beta testing. The Windows version officially released on July 9, 2013, through Steam, Valve’s digital distribution platform. Versions for OS X and Linux followed on July 18, making the launch broader than a Windows-only release.
Dota 2 grew out of Defense of the Ancients, a community-created Warcraft III mod. Valve hired the mod’s lead designer, IceFrog, in 2009 to develop a standalone version. Steam provided the distribution, account, update, matchmaking, and online-service infrastructure for the new game.
A common mix-up is confusing Dota 2’s origins with its release platform. Warcraft III was the home of the original mod, but Dota 2 itself was not released through Battle.net. Epic Games Store and GOG.com also were not the platform named in the question. Dota 2 launched as a free-to-play Steam title and remains closely associated with Valve’s PC ecosystem.