25% of Compendium revenue goes to The International prize pool.
Valve introduced the Compendium for The International 2013 as an in-game tournament companion and crowdfunding mechanism. Players bought the digital product for predictions, collectibles, challenges, and other tournament-themed rewards; one quarter of its revenue was added directly to the event’s base prize fund.
That formula helped turn The International into esports’ signature prize-pool story. The 2013 event’s pool grew beyond $2.8 million, while The International 2021 eventually reached about $40 million. The contribution is commonly described as 25% of Compendium revenue, not 25% of every Dota 2 purchase or of the tournament’s entire income.
A related source of confusion is that Valve’s monetization changed over time. The Compendium and battle-pass systems have been redesigned, and later Internationals did not always follow the same commercial structure. For the historical quiz fact, however, 25% is the canonical figure associated with the Compendium crowdfunding model.