Core Concepts
Prediction markets let you trade contracts whose value depends on the outcome of a defined event. The contract is not the underlying asset itself: it is a time-bound position on whether a particular proposition resolves Yes or No.
The mental model
Think of a prediction market as a question with tradable answers:
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- Event — The question being resolved, including its rules, timing, and resolution source. Examples include “Will BTC settle at or above $100,000?” or “Which team will win this game?”
- Contract — A tradable instrument associated with one proposition within an event. The instrument is defined in YES space: its label, ticker, and symbol identify what resolving YES means. An event can have multiple contracts, such as one contract for each team in a winner market.
- Outcome — The side of a contract:
yesorno. The outcome describes the exposure represented by the position, not the direction of the order. Buying and selling are order directions;yesandnoare outcomes on the instrument. - Position — Your quantity of a contract outcome. A position can be opened, reduced, or closed by trading the corresponding instrument.
The event defines the broader question. The contract defines one YES-space proposition you can trade. The outcome defines whether you hold YES or NO exposure to that proposition.
To discover events and inspect their contracts, use List Events and Get Event. For ticker construction and category-specific formats, see Ticker Overview.
YES and NO positions
For a binary contract, YES and NO are complementary outcomes on the same tradable instrument:
| Position | Resolves to a payout when the event... |
|---|---|
| YES | Resolves in favor of the stated proposition |
| NO | Does not resolve in favor of the stated proposition |
For example, consider an event containing this contract:
Will the Federal Reserve lower its target rate by at least 0.25% at the specified meeting?
The API may return this instrument:
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Buying the yes outcome expresses that the contract proposition will resolve YES. Buying the no outcome expresses that it will resolve NO. Both orders use the same YES-space instrumentSymbol; the order's outcome field selects the exposure. If the contract resolves YES, the YES outcome pays its defined settlement amount and the NO outcome does not. If it resolves NO, the reverse is true. Always use the event's resolution rules and contract metadata as the source of truth for settlement.
instrumentSymbol
instrumentSymbol is the complete, exchange-recognized identifier for a tradable prediction-market contract. It commonly includes the GEMI- prefix, the event identifier, and the contract's YES-space proposition suffix:
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Use the returned instrumentSymbol when requesting market data or placing and managing orders. Do not infer a symbol by concatenating values from an event unless the ticker format for that market supports it; instead, discover the contract through the event APIs and use the symbol returned by Gemini. The Ticker Overview describes structured ticker formats and their exceptions.
Price as market-implied probability
Prediction-market prices are quoted in the contract’s settlement currency. For a binary contract with a settlement value of $1, a YES price of $0.65 is commonly read as a market-implied probability of approximately 65%:
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This is an interpretation of the current market price, not a guarantee that the event has a 65% objective chance of occurring. Public order-book depth is normalized in YES space. For NO notional derived from that book, use the complementary price, 1 - yesPrice. The price reflects the participants and liquidity available in the market and can change as orders are placed and filled. Bid-ask spread, fees, order-book depth, and the timing of the quote also affect the price you can actually trade.
For the complementary NO outcome, the implied probability is approximately the remaining probability. In practice, YES and NO prices may not add to exactly $1.00 because of spread, fees, and temporary market imbalance.
The settlement value and resolution rules come from the event and contract definition. Read those definitions before interpreting a price or comparing it with an external probability estimate.
Prediction contracts versus underlying assets
A prediction-market contract can refer to an underlying asset such as BTC, ETH, a commodity, or a sports team, but it does not give you ownership of that asset.
| Prediction-market contract | Underlying asset ownership |
|---|---|
| Exposure is to a defined event outcome | Exposure is to the asset’s market value or ownership rights |
| Usually settles to a fixed amount according to the contract rules | Value generally changes continuously with the asset or its rights |
| Does not represent units of BTC, ETH, a commodity, or another physical or financial asset | Represents the asset itself or a claim on it |
Is identified and traded with a prediction-market instrumentSymbol | Uses the asset’s own market, symbol, and custody or settlement rules |
For example, buying the YES outcome of a BTC-linked prediction contract does not buy BTC and does not create a BTC balance. It creates exposure to whether that contract resolves YES. The contract can lose value even if BTC rises when the exact threshold or resolution condition is not met; conversely, it can resolve YES without giving you any BTC.
Before trading, use List Events to find available events, Get Event to read the event and contract definitions, and Ticker Overview to understand the corresponding symbols.