The update - which has been piloted for almost a year and follows on from the existing Polls feature - lets users compete in a tournament-style game by guessing the outcome of award ceremonies, sporting contests and other events.
Although people are competing for bragging rights - there's no actual money involved - Reddit has teased that Premium members could "get special advantages or benefits in the future".
Only moderators can post tournaments, which feature a series of questions for users to bet on.
Every participant gets 1,000 free tokens to answer, and a right answers gets them a share of the winning, while losing all their tokens takes them out of the competition.
Reddit explained: "Predictions are a fun way for redditors to compete against each other and gain status by predicting the outcome of future events.
"Communities can create prediction questions and tournaments on just about any future event such as who will win the Best Picture award at the next Oscars ceremony or which popular character will die first in George RR Martin’s next book. "