7 Best Prediction Market APIs and SDKs in 2026

The best prediction market APIs in 2026 do more than expose one exchange. The same events now trade across Polymarket, Kalshi, Opinion, Limitless, SX Bet, Myriad, and Gemini, each with its own identifiers, price formats, and order-book schemas. For developers, traders, AI agents, and financial institutions, the challenge is no longer finding a prediction market. It is accessing reliable, comparable data across venues without maintaining a separate integration for every platform. Smaller venues are worth a look too, including the SX Bet API.

This guide ranks the top 7 prediction market APIs and SDKs in 2026 by venue coverage, real-time data, historical depth, execution support, and SDK quality, and shows where each one fits in a modern stack.

Disclosure: Predictefy is our product, and it sits at #1 on this list. Every claim about the other providers comes from their official documentation, and each of their entries includes an honest limitation. Verify details against each venue's docs before you build; this space moves fast.

The 7 Best Prediction Market APIs at a Glance

1. Predictefy: Best for Cross-Venue Matched Markets and Arbitrage

Predictefy is the cross-venue layer of this list: a prediction market terminal and data platform that puts every major venue in one place, matches identical markets across platforms, and normalizes prices, outcomes, order books, volume, and liquidity into one consistent schema. Coverage spans 12 venues, including Polymarket, Kalshi, Opinion, Limitless, SX Bet, Gemini, Myriad, Predict.fun, Probable, Rain, Alpha Arcade, and Hyperliquid.

Strengths:

• The only entry on this list built around matched markets: Compare Mode groups markets representing the same question across venues, which is the capability everything else in this article, from price comparison to arbitrage, depends on.
• A live arbitrage feed that streams matched-market price gaps across venues, including spread, size, liquidity, and route data, usable for trading systems, bots, and dashboards.
• One normalized schema across all covered venues, so cross-venue work does not require venue-specific code.
• Historical OHLCV, price, volume, and liquidity data dating back to 2020 across leading venues.

Getting started: the developer surface is public and self-serve. The full API reference is at docs.predictefy.com, the TypeScript and Python SDKs and an MCP server install from npm and PyPI, and plans are published from a free tier with no invite, with the arbitrage feed on Builder at $48.88 a month. The REST API works with only an API key, so a first call needs no package install.

Best for: traders, researchers, and teams that want matched markets, normalized cross-venue data, and arbitrage signals without building and maintaining a dozen venue integrations.

2. Polymarket: Best for Deep Liquidity and Crypto-Native Order Books

Polymarket is the venue most people mean when they say "prediction market." It runs a central limit order book with off-chain matching and onchain settlement on Polygon, and it is widely cited as the volume leader in the space. For developers, the standout feature is that market data is genuinely free: REST reads are public, and the WebSocket market channel streams order books, price changes, and trades with no API key at all.

Strengths:

• Deepest order books and broadest event coverage of any single venue: politics, sports, crypto, and current events.
• Fully public market data, including an unauthenticated WebSocket market channel.
• Price history and timeseries endpoints for research, plus EIP-712 signed trading from your own wallet.

One thing to get right in 2026: CLOB V2 went live on April 28, and the V1 infrastructure was retired at the end of June once the forced migration window closed. V1 SDKs and V1-signed orders no longer work. The SDK advice has already moved once since that cutover, which is the part worth re-checking: the cutover-era py-clob-client-v2 remains supported, but at the time of writing Polymarket points new projects at its newer unified client, polymarket-client, so read the SDK section of docs.polymarket.com before you pin a dependency. US users are served by a separate CFTC-regulated exchange, Polymarket US, which keeps its own documentation at docs.polymarket.us and a different auth model.

Limitations: "Polymarket" is now effectively two platforms with incompatible APIs, and the V2 cutover showed that breaking changes ship on their schedule, not yours. It is also a single venue: deep, but only one view of any given event.

Best for: traders who want the deepest books and free streaming data, and are comfortable with wallet-based signing.

3. Kalshi: Best for Regulated US Event Contracts

Kalshi is a CFTC-regulated exchange where event contracts trade in cents and a matched YES and NO pair always sums to $1.00. It has the most institution-shaped API on this list: REST v2, WebSocket streaming, and a full FIX API, which no other venue here offers.

Strengths:

• The only CFTC-regulated venue among the seven ranked here, with USD settlement and exchange-operated clearing.
• Strong historical data: candlesticks at 1-minute, 1-hour, and 1-day intervals, plus a dedicated historical namespace.
• Official Python and TypeScript SDKs, and FIX connectivity for existing institutional trading infrastructure.

Authentication is stricter than the crypto venues: requests are signed with an API key ID and per-request RSA signatures, and the WebSocket requires authentication at the handshake even for public channels. The REST order book endpoint is public, though, like the rest of Kalshi's market data, which really is free and keyless. So there is a zero-signup route to depth, just not to streaming; you create an account and keys before you open a live stream. The official Python client also ships as separate sync and async packages and, at the time of writing, wants a recent Python release (3.13 or newer), which is worth checking against your runtime before you commit. Kalshi documents the current requirements at docs.kalshi.com.

Limitations: the regulation that is Kalshi's selling point also narrows it. It lists only what a US-regulated exchange can list, so its market universe is smaller than the crypto-native venues, and the auth model adds real integration friction compared to Polymarket's open reads. One detail to update if you last read about Kalshi a year ago: it began expanding outside the US during 2026, starting with Brazil, so calling it a purely domestic venue is no longer accurate, even though its listings still answer to a US regulator.

Best for: US firms that need a regulated counterparty, settle in dollars rather than stablecoins, or want FIX connectivity.

4. PMXT: Best for One SDK Across Many Venues

PMXT is to prediction markets what CCXT is to crypto exchanges: an open-source, MIT-licensed SDK (pip install pmxt) that wraps many venues behind one interface. If your problem is "compare the same event across venues without writing six API clients," this is the shortest path. For a direct comparison on venues, limits and commercial use, see Predictefy vs PMXT.

Strengths:

• Normalized market data across 10+ venues through a single interface.
• Unified OHLCV from 1-minute to 1-day intervals, archive snapshots, and WebSocket order books and trades.
• Open source and free to self-host.

The catch is the asymmetry between reading and trading. Data coverage spans 10+ venues, while hosted order placement covers three, Polymarket, Opinion, and Limitless, and self-hosting adds venue-native writes such as Kalshi with your own credentials. A unified abstraction also hides venue-specific features by design; you will not reach Kalshi's FIX API or Limitless's NegRisk groups through a common interface. The hosted mode routes funds through PMXT's own custody and escrow, which is a different trust model than signing from your own wallet, so read that part of the docs before depositing.

Limitations: maturity. It is a young open-source project, and the venues underneath it ship breaking changes (see Polymarket's V2 cutover) that the SDK has to chase.

Best for: cross-venue research and arbitrage scanning, with direct venue APIs held in reserve for execution.

5. Limitless: Best for Fast-Settling Hourly and Daily Crypto Markets

Limitless runs on Base and specializes in short-duration markets: hourly and daily contracts on crypto prices that settle fast enough to trade like an options book. Shares are priced from $0.01 to $0.99 in USDC, with every YES-NO pair fully collateralized by $1.00.

Strengths:

• The broadest SDK coverage on this list: official clients in Go, Python, Rust, and TypeScript.
• Varied market structure: a CLOB, an AMM, and NegRisk groups for mutually exclusive outcomes.
• Price-history endpoint with configurable intervals, and fast settlement that suits high-frequency strategies.

One gotcha worth knowing before you build a backtest: the oracle candlesticks endpoint returns the Chainlink price of the underlying asset, not candles for the prediction market itself. They answer different questions, and confusing them will quietly corrupt your research. If TypeScript is your stack, the arbitrage SDK quickstart gets you to a first query quickly.

Limitations: markets that live for an hour accumulate an hour of history, so long-horizon research data is structurally thin, and coverage concentrates in crypto prices rather than broad event categories. It is also a single venue on a single chain.

Best for: traders of short-term crypto price action who want low-level SDK support in a systems language.

6. Opinion: Best for Typed CLOB SDKs and Polymarket-Compatible Schemas

Opinion is a CLOB venue on BNB Chain whose API is deliberately shaped like Polymarket's: its price-history endpoint is documented as returning a "Polymarket-compatible format," which makes it one of the easier second venues to add once you have a Polymarket integration running.

Strengths:

• Full CLOB trading with typed Python and TypeScript SDKs.
• Price history at 1-minute, 1-hour, 1-day, 1-week, and max intervals, plus orderbook and latest-price endpoints.
• Polymarket-compatible schemas that reduce porting work.

The most important integration detail is authentication: the public data endpoints for markets, order books, latest prices and price history need no API key, while every other endpoint takes an apikey header and the WebSocket needs the same key. You create that key yourself with a wallet signature, with no application form to wait on.

Limitations: the main one is resolution. Opinion settles markets through an AI oracle, a newer and less battle-tested mechanism than CFTC-regulated clearing or Polymarket's onchain resolution, and it is the piece to scrutinize before putting size on.

Best for: teams that already speak Polymarket's schema and want BNB Chain exposure.

7. SX Bet: Best for Sports Markets with Back and Lay Depth

SX Bet is the specialist of this list: a peer-to-peer sports exchange where you can both back and lay outcomes, running on its own chain, the SX Rollup, with USDC collateral. Odds move on a fixed 0.125% ladder, and orders are EIP-712 signed.

Strengths:

• Open market data: market discovery, the per-market order book snapshot and the public trade tape need no API key. On the V3 API an x-sx-api-key header is required for orders, balances, best odds and the realtime token, and the realtime feed runs over Centrifugo WebSockets.
• True exchange mechanics for sports: back and lay both sides with visible P2P depth.

Two things to know before integrating. First, there is no candlestick or OHLCV endpoint; historical data means paginated trade history, so if you want candles you build them yourself from trades. Second, the realtime stack migrated from Ably to Centrifugo, and older tutorials that reference Ably are stale.

Limitations: scope. SX Bet does sports and only sports, so it cannot be your only integration for general event markets, and the build-your-own-candles situation makes historical research more work than on Kalshi or Opinion.

Best for: sports quants who want exchange-style back and lay depth with genuinely open data access.

How to Choose a Prediction Market API

The best prediction market APIs generally perform well across seven areas.

1. Venue coverage

Single-venue APIs are useful for applications focused on one exchange. Multi-venue APIs suit aggregators, institutional systems, arbitrage tools, and cross-market research. Teams buying for a desk rather than a side project should weigh these against what an institutional prediction market API needs to do.

2. Real-Time Data and WebSocket Feeds

Prices in active prediction markets move fast during live sports, elections, economic announcements, and breaking news. WebSocket feeds or low-latency streaming matter for trading systems, alerts, and market making.

3. Normalized schemas

Every venue represents markets differently. A normalized API converts prices, outcomes, timestamps, liquidity, volume, and market status into one consistent format, reducing the venue-specific code you maintain.

4. Matched Markets and Cross-Venue Arbitrage

Cross-venue matching identifies when two differently named contracts represent the same or economically equivalent outcome. It is what makes arbitrage, price comparison, smart order routing, and aggregation possible.

5. Prediction Market Historical Data

Backtesting, research, model development, and AI training all need history: OHLCV candles, tick-level trades, order-book snapshots, price history, resolution data, and cross-venue spreads. Our guide to prediction market data sources goes deeper on what each venue keeps and where the gaps are.

6. Trading and execution

Data access gets you research; execution support turns a signal into a position. Check whether the API covers the full order lifecycle: place, cancel, and amend orders, plus fill notifications over WebSocket rather than polling. Look at the signing model too, because it determines your infrastructure. Crypto-native venues like Polymarket, Limitless, and SX Bet use EIP-712 wallet signatures, while Kalshi uses API keys with per-request RSA signatures and offers FIX for institutions. Finally, check what custody the API assumes: self-custodied wallet signing, exchange-held balances, and third-party escrow are very different risk profiles.

7. Documentation and SDK support

Clear documentation, typed SDKs, working examples, authentication guides, and stable schemas substantially reduce integration time.

What Is a Prediction Market API?

A prediction market API is an interface that lets software programmatically access data or trading functionality from one or more prediction market platforms, instead of a human reading a website. Venue-specific APIs give deeper access to one exchange; multi-venue APIs give broader coverage through a single integration.

Developers use prediction market APIs to build:

Why Prediction Market APIs Matter in 2026

Prediction market liquidity is increasingly fragmented. The same event may trade simultaneously on Polymarket, Kalshi, Opinion, Limitless, SX Bet, Myriad, and Gemini. However, each platform exposes that market through a different interface:

This fragmentation creates technical complexity. A team building directly against five venues maintains five data pipelines, five schemas, five change logs, and five sets of trading logic. It also makes cross-venue analysis difficult: two markets can represent the same real-world event with completely different titles, outcome labels, and expiration times. The most valuable prediction market infrastructure therefore does more than retrieve markets. It normalizes, matches, compares, and routes data across venues.

How Prediction Market Arbitrage Works Across Venues

The same real-world event often trades on three or four venues at once. A Fed rate decision might be priced at 62 cents on Kalshi, 0.65 on Polymarket, and 1.56 decimal odds on a sports-style exchange. Those are three notations for the same thing: an implied probability. Cross-venue arbitrage starts by normalizing every venue's price format into one probability scale, then looking for gaps large enough to survive fees.

The cleanest structure is a synthetic lock: buy YES on the venue where it is cheap and NO on the venue where it is expensive. If the two legs together cost less than the $1.00 the pair pays out, the gap is your margin on paper, whichever way the event resolves. In practice the edge is rarely that clean, and the hard problems are operational rather than mathematical:

• Matching markets. Venues title the same event differently, and near duplicates with subtly different resolution criteria are the classic trap. "Fed cuts in September" and "Fed funds rate below 4.00% on Oct 1" are not the same contract.
• Resolution risk. Kalshi settles under CFTC-regulated rules, Polymarket through onchain resolution, Opinion through an AI oracle. Two venues can disagree on the outcome of the "same" event, which turns a lock into a directional bet.
• Capital fragmentation. Each leg needs collateral on a different chain or exchange: USDC on Polygon, dollars at a US exchange, USDC on Base. Rebalancing costs time and bridge fees.
• Execution timing. Gaps close fast. By the time a human fills the second leg, the first venue has often repriced.

This is why arbitrage across prediction markets is effectively an API problem. You need streaming order books from every venue, a reliable mapping of matched markets, and programmatic execution on at least two of them, all running continuously. We break the mechanics down further in our guide to prediction market arbitrage.

Frequently Asked Questions

Conclusion

There is no single best prediction market API in 2026, because the market itself refuses to consolidate. Polymarket has the liquidity, Kalshi has the regulator, Limitless has the settlement speed, SX Bet has the sports depth, and none of them speak the same language. Even the aggregation layer is unstable: Dome, a unified prediction market API, was acquired by Polymarket in February 2026 and shut down in April, and Polymarket's own V2 cutover retired every V1 integration in production. The venue list keeps growing at the same time. DraftKings opened its own exchange, DKeX, on 26 June 2026 on a CFTC licence it acquired with Railbird, which is one more set of identifiers and schemas for anyone doing cross-venue work to absorb.

So choose by constraint, not by ranking. If you need a regulated US counterparty, start with Kalshi. If you need depth and free data, start with Polymarket. If your strategy only works across venues, start with a unified layer and keep direct venue access for execution. And whatever you pick, treat the docs as a moving target: every claim in this article was verified against official documentation at the time of writing, and this space has already proven it can break an integration in a single quarter.

None of this is financial, legal, or tax advice. Which venues you can legally access, and what they cost you, depends on where you live, and both move without much warning.