Valve has announced a 20 player, 10 vs. 10 custom game coming to Dota 2 next week. The 20-player mode was revealed at The International, where 10 professional players played alongside 10 players selected from the audience.
It was nonsense in all the right ways.
The mode was played in the Dota 2 Reborn/Source 2.0 client, where custom games have become quite popular.
This is the first new mode Valve itself has introduced to Dota 2 since the Year Beast Brawl.