About Prophet Markets

Prophet Markets is a play-money prediction market we run for the AI Forecasting Workshop at ICML 2026. You get fake cash and bet it on real questions: who wins a World Cup match, which paper takes Best Paper, that sort of thing. Nobody risks real money. What’s at stake is your standing in the room, plus a few prizes at the end.

You start with $50 in play money — another $50 if you scan the QR at the workshop. Each market is a question with a few possible answers, and you buy shares in whichever answer you believe in. If that answer turns out right, every share you hold earns you $1; if it’s wrong, it’s worth nothing. A share’s price is just the room’s guess at the odds — so you make money by buying answers you think are underpriced and selling once the room catches up. Your score is your cash plus whatever your open positions are worth right now.

How does the price move when you trade? →

One thing: please trade it yourself. We discourage bots — this one’s for humans to have fun with.

Behind each market is an automated market maker — a small program that always quotes a buy and a sell price on every outcome. That’s why you never have to wait for someone to take the other side: there’s always a price to trade against, even on a market that just opened with nobody else in it.

It isn’t a house deciding the odds. The maker follows a fixed rule — the more people buy one outcome, the more it nudges that price up (and the others down), so the price keeps tracking how the room is betting. A big bet moves it more than a small one; that’s the whole point of a market. (The math is the LMSR rule, if you want the textbook name.)

And you can be the market yourself: post a limit order at your own price and it rests on the book right beside the maker, for anyone to trade against. Real orders and the maker sit side by side, and you always get the best price showing.