Provider shortlist
Licence summaries are plain-language readings of vendor terms, not legal advice. Prices are as listed on the read date. Narwhal API is owned and operated by Nusantara Ventures, LLC.
Narwhal API
Probabilities for economic data, central bank, metals and energy topics, normalised across both venues.
Predexon
Deep Polymarket and Kalshi tick history, delivered as bulk Parquet files.
PolymarketData
Polymarket history with one-minute order books and bulk exports in Parquet, CSV or JSON.
Oddpool
Existing accounts that want free Kalshi and Polymarket history and canonical cross-venue IDs.
Kalshi API
Primary-source Kalshi markets, trades and candlesticks of 1 minute, 1 hour and 1 day.
Polymarket API
Primary-source Polymarket price history and trades, public with no key.
FinFeedAPI
Raw order book events and trades from nine exchanges, as flat files by day or time range.
Tatum
Candles for Polymarket and Kalshi in one schema, for light studies that need no bulk file.
Compare the options
Best fit is not feature parity. Check the evidence and limitation together.
| Provider | Best for | Evidence checked | Important limitation |
|---|---|---|---|
| Narwhal API | Probabilities for economic data, central bank, metals and energy topics, normalised across both venues. | Free covers 12 months of history, Basic 5 years and Pro full history with first-reported and as-of values. Pro costs $149 for 1,000,000 requests. | Coverage stops at those topic groups. Plans list no bulk export, and the Free tier serves the previous day's close. |
| Predexon | Deep Polymarket and Kalshi tick history, delivered as bulk Parquet files. | Ticks start 2 March for Polymarket and 5 March for Kalshi. Polymarket costs $40 per GiB and Kalshi $80, with a $5 minimum per download. | Cross-venue matching endpoints were removed on 20 July. Its terms bar unauthorised resale and are silent on publishing derived data. |
| PolymarketData | Polymarket history with one-minute order books and bulk exports in Parquet, CSV or JSON. | Standard history starts in August 2025. Ultra costs $360 a month for unlimited history; Trader costs $60 for one month of history. Yearly billing is 25% off. | Polymarket only. Terms permit journalism and academic work but bar capital market clients and data distributors, and cap output at limited excerpts. |
| Oddpool | Existing accounts that want free Kalshi and Polymarket history and canonical cross-venue IDs. | History starts 19 March for Kalshi and 20 March for Polymarket. Its enterprise Reference Data API joins events across venues. | New subscriptions are closed. Data is licensed for personal, internal use, with no commercial redistribution or caching for redistribution. |
| Kalshi API | Primary-source Kalshi markets, trades and candlesticks of 1 minute, 1 hour and 1 day. | Settled markets, candlesticks and trades older than a rolling cutoff move to historical endpoints. Its docs list no historical order book. | The Developer Agreement bans collecting, caching or storing API data except for your own Kalshi trading, and sharing it without written authorisation. |
| Polymarket API | Primary-source Polymarket price history and trades, public with no key. | The prices-history endpoint takes intervals from 1m to max. Its docs point to Goldsky, Dune and Allium for bulk on-chain history. | It offers no order book history. Written terms for publishing API data were not confirmed in this review, so ask Polymarket first. |
| FinFeedAPI | Raw order book events and trades from nine exchanges, as flat files by day or time range. | OHLCV bars run from one second to five years. Credits cost $1 pay-as-you-go and $0.65 at the 1,024 tier. Start dates are not stated. | The Customer Agreement allows internal business purposes only, and the customer carries any extra licences the data sources require. |
| Tatum | Candles for Polymarket and Kalshi in one schema, for light studies that need no bulk file. | OHLC candles run from 1m to 1w, and a source flag picks candlesticks or midpoint. Price history costs 200 credits a call; Free has 100,000 credits. | History depth is not stated and there is no bulk export. Terms on redistributing the data were not found in this review. |
Choose by requirement
Check the licence before the data
Most prediction market data comes with strings. Kalshi bans caching or storing API data except for your own trading. Oddpool licenses personal internal use. FinFeedAPI allows internal business purposes only. Predexon bars resale and says nothing on publishing derived data. PolymarketData permits journalism and academic work. Narwhal's Free tier includes commercial app use, but confirm publication rights in its terms before you quote results. Write to the vendor before a paper or article relies on stored data.
Kalshi's rule on stored data
Section 3.1 of the Kalshi Developer Agreement prohibits collecting, caching, aggregating or storing data from the API except to help your own trading on Kalshi, and bars sharing it with third parties without written authorisation. A paper that builds a dataset straight from the Kalshi API therefore needs permission. Use of the API also requires a Kalshi member account under section 4.1. Kalshi can also change or cut rate limits at its sole discretion, so a long collection job should expect interruptions.
Journalists and academics
PolymarketData names personal research, academic research and journalism as permitted uses, and internal analytics for organisations that are not capital market clients. It bars broker-dealers, funds, prop firms, banks and capital-markets fintechs. Permitted output must be real analysis with limited, insubstantial factual excerpts and attribution where practicable. That is the clearest written position among these vendors, though it covers Polymarket only. If your employer touches capital markets, ask PolymarketData in writing before you subscribe.
How far back each source goes
PolymarketData starts in August 2025 and puts older history on enterprise plans. Predexon claims trade and price history back to 2020, with tick data from March and free REST order books from January. Oddpool's history begins in March. Kalshi splits live and historical endpoints at a rolling cutoff. Narwhal gives 12 months on Free, 5 years on Basic and full history on Pro. Tatum and FinFeedAPI do not state a start date, while Polymarket's own prices-history endpoint accepts a max interval and needs no key.
Price per history
Predexon prices ticks by volume: a full Polymarket day runs near 13 GiB, about $520 at $40 per GiB, and a Kalshi day costs $250 to $400. It gives $50 in credits when you add a payment method. PolymarketData charges $60, $120 or $360 a month for one month, three months or unlimited history. FinFeedAPI sells credits at $1 down to $0.65. Narwhal Pro is $149 a month. Predexon's $5 minimum applies to each download, and downloads above $100 need a prior quote.
Bulk export
Predexon delivers Parquet files with zstd compression, finalised at 06:00 UTC the next day, up to 31 days per request through a signed link. PolymarketData offers S3 dumps in Parquet, CSV or JSON, once or on a schedule. FinFeedAPI serves flat files by day or time range. Oddpool restricts dumps to Enterprise. Kalshi and Polymarket offer none, and Narwhal plans list no bulk export, so plan to page through the API. Polymarket's docs send bulk on-chain history to Goldsky, Dune and Allium.
Cross-venue matching
Predexon switched off its matching endpoints on 20 July; they return 410 Gone. Oddpool's canonical IDs sit in an enterprise-only Reference Data API, and in its own sample of 250 matched events about a third were settlement-fungible. FinFeedAPI and Tatum describe no same-event matching. Narwhal groups both venues under one topic, such as an Australian central bank decision, but only for its economic, central bank, metals and energy topics. OddsPapi assigns one fixture ID across sportsbooks and prediction venues, for sports only.
Resolution and settlement data
Resolution wording differs by venue, so matching needs care. Kalshi keeps settled markets under its historical endpoints. Predexon includes an endpoint family for the UMA oracle. Oddpool tags each matched pair with a settlement-fungibility class. Narwhal topics carry a resolution kind, such as a data release, which suits studies of how odds move before a scheduled number. Oddpool's own sample found only about a third of matched events settled identically. Read both rulebooks before treating two contracts as one.
Vendors that closed
Dome ended on 28 April after its acquisition by Polymarket. Oddpool no longer accepts new subscriptions, though existing and free accounts continue. Predexon removed cross-venue matching on 20 July and ended order placement on 10 July. A study that depends on one of these needs a stored copy where the licence allows it. Record the date you pulled each series, since endpoints can disappear, as Predexon's matching service did. Traders can read the companion page for live feeds.
Free routes into the data
Predexon's REST order book history is free and unlimited, from 1 January for Polymarket and 7 January for Kalshi, and its trade and candlestick endpoints do not count toward quota. Polymarket's prices-history and Data API v2 need no key. PolymarketData Free gives one month at 10-minute granularity without order books. Oddpool's free tier includes history but is closed to new accounts. Narwhal Free covers 12 months of history within 5,000 requests a month, with a daily close on odds.
Each detailed provider page lists the first-party documentation used, its evidence boundaries, and its review date. Reviewed: