Prediction markets API

What is a prediction market's open interest, and how many holders and trades?

Contracts open right now and lifetime volume (Kalshi), or lifetime volume, distinct holders and trade count (Polymarket), for one market. Counts, not USD.

GET/api/external/prediction/prediction-market-open-interest/{id}

Get a free API key Try it in the API reference

What it returns

openInterest is the number of contracts open right now, each paying $1 if its outcome wins; volume is the lifetime amount traded, in contracts on kalshi and in outcome shares on polymarket. Neither is a USD figure. What each venue publishes differs: a kalshi market has openInterest and volume but no holders or trades (always null); a polymarket market has volume, holders and trades but no openInterest (null, with openInterestUnavailableReason saying why). holders counts distinct wallets that have held one of the outcome tokens, not only those holding now. A closed market keeps its last figures. asOf is when the figures were last updated and can be hours old while stale is false. An id of neither venue's shape is a 400; a well-formed one no market has is a 404.

Chains

This endpoint is not tied to a chain: it takes no chain in its request.

Request

Send your key in the x-dex-data-key header. Replace each <placeholder> with a real value.

curl -H "x-dex-data-key: $DEXDATA_API_KEY" \
  "https://api.dexdata.io/api/external/prediction/prediction-market-open-interest/<id>"

Parameters
Parameter	Description
`id` path · string · required	A prediction-market id, e.g. "<marketAddress>:Polymarket:<exchangeAddress>:<networkId>" or "<slug>:Kalshi" — not a token mint or contract address, and not scoped to any chain this API otherwise supports.

Response fields

A JSON response. Every field is always present; null means the value could not be established, never zero.

Response fields of What is a prediction market's open interest, and how many holders and trades?
Field	Type	Description
`marketId`	string	The market `id`, as passed.
`venue`	string	The venue the market trades on.
`openInterest`	number \| null	Contracts open right now, each paying $1 if its outcome wins. Not USD. Null on `polymarket`.
`volume`	number \| null	Lifetime amount traded: contracts on `kalshi` (whole numbers), outcome shares on `polymarket` (fractional). Not USD.
`holders`	integer \| null	Distinct wallets that have held an outcome token of this market, including those that no longer do. Null on `kalshi`.
`trades`	integer \| null	Lifetime number of trades. Null on `kalshi`.
`asOf`	string \| null	When the figures were last updated, ISO 8601 UTC. Null when unknown.
`stale`	boolean \| null	True when the figures are known to be out of date; null when unknown.
`estimated`	boolean \| null	True when the figures are an estimate rather than a reading; null when unknown.
`openInterestUnavailableReason`	string \| null	Why `openInterest` is null, as a snake_case code, e.g. `official_open_interest_not_indexed`. Open set. Null whenever `openInterest` is published.

Price per call

Every call: 18 credits

Charged only when the call succeeds. Prices as of 2026-10-30; the current ones are always in the API reference.

One prediction market's state and live outcome prices
The market's question, prices and USD volume, alongside its open interest and holder count.
The full category taxonomy prediction markets are sorted under
The taxonomy prediction events are filed under. Read it to learn the vocabulary an events query can filter by; it answers no question about any one event.
One prediction-market event's identity, lifecycle and windowed stats
One event: what is being bet on, whether it is open or settled, and its windowed activity. The markets that price it are a separate read.
Prediction-market events, ranked by volume, liquidity or trending score
A ranked page of prediction EVENTS -- the question being bet on, one level above the markets that price it. Use it to find an event id; it prices nothing.
A prediction event's volume, liquidity and open interest over time
How trading on a whole prediction event moved bucket by bucket — volume, trades, traders, and liquidity and open interest as OHLC — across all of its markets.
One prediction market's OHLC-style bars over a bounded window
The priced series for one market over a bounded window, in OHLC-style bars. A different question from the market's state: how the price moved, not what it is.

Start building with DexData today

Sign in, create a key and make your first call in a minute. Free credits every month, and you only pay for calls that succeed.

Get a free API key