Best Prediction Markets for Arbitrage in 2026

Ask which prediction market is best for arbitrage and you'll usually get a list of the biggest venues. Size matters, but it isn't the whole answer. Arbitrage means buying both sides of the same event on two venues for less than the $1 the winning side pays out. So the real question is which venues give you the right pair: deep books that disagree often enough, fees that leave something over, rules that settle the same way, and an API fast enough to act before the gap closes.

This guide ranks the prediction markets that matter for arbitrage in 2026, shows the pairs worth running, and covers the traps that turn a paper arb into a loss. If you're new to the strategy itself, start with our guide to prediction market arbitrage and come back.

What Makes a Prediction Market Good for Arbitrage

Six things decide whether a venue is worth connecting:

• Fees at the prices you trade. Most prediction markets now charge takers a fee shaped like p × (1 − p), which peaks at 50 cents. A venue that's cheap on a 90-cent favorite can be expensive on a coin flip.
• Order book depth. A 3-cent gap on 50 contracts is not the same trade as a 3-cent gap on 5,000. Thin books mean slippage on the second leg.
• API access. Cross-venue gaps often last seconds. Without an API and a WebSocket price feed, you'll see arbs after they're gone.
• Overlap with other venues. A venue only helps if others list the same events. Sports, economic data and big political races overlap the most.
• Settlement rules. Two contracts that look identical can settle differently on a tie, a postponement or a cancellation. It's the biggest hidden risk in prediction market arbitrage.
• Who can open an account. Every venue restricts some countries or states. The best pair on paper is useless if you can't legally hold both accounts.

The Best Prediction Markets for Arbitrage, Ranked

1. Kalshi: The Anchor for Almost Every Setup

Kalshi is a CFTC-regulated exchange and the clear volume leader. The Block puts its August 2026 volume at more than $37 billion, and sports make up the large majority of it. For arbitrage, three things stand out. The depth means your second leg is less likely to move the price. The API is complete: REST, WebSocket and FIX, with keys available to any account and a basic tier of about 20 reads and 10 writes per second. And the fee formula is published.

Kalshi taker fee = roundup(0.07 × contracts × price × (1 − price)), rounded up to the cent.

That works out to about 1.75 cents per contract at 50 cents and about 0.63 cents at 90 cents. Some series also charge makers (a quarter of the taker rate, on major sports and on Fed and CPI markets), and some use a lower multiplier, so check the series before you model a trade.

Access is the catch. US residents 18 and over can sign up with ID verification, and Kalshi now accepts many non-US users, but it restricts 55 jurisdictions, including the UK, Canada, Australia and India. Inside the US, court rulings in several states, including Massachusetts, Michigan, Washington and Nevada, have restricted some Kalshi markets there. As an exchange, Kalshi has no reason to cut winning traders, which is why prediction markets don't limit winners the way sportsbooks do.

2. Polymarket (International): The Deepest Second Leg Outside the US

The international Polymarket is an offshore order book settled in pUSD, a Polygon token backed one to one by USDC that replaced USDC.e in April 2026. It traded about $4.6 billion in August, and its public REST and WebSocket APIs are built for automated trading, with orders signed by your wallet.

Fees are no longer zero. Since the early-2026 rollout, takers pay contracts × fee rate × p × (1 − p), with the rate set per market: 0.05 for most sports, economics, culture and weather markets, 0.04 for politics, finance and tech, 0.07 for crypto and 0 for geopolitics. Makers pay nothing and get a share of taker fees back as rebates. Some markets still show a zero rate, so read the fee on each market instead of assuming one.

Two details matter for arbitrage. Live sports markets add a short order delay (about a second on the markets we checked) during which you can't cancel, and crypto markets add a 150-millisecond taker delay. And access is the hard limit: the US, UK, France, Germany, Italy, Poland, Australia, Singapore, Brazil and several other countries are close-only, so residents there can't open new positions.

3. Polymarket US: The US Trader's Second Venue

Polymarket US is a separate, CFTC-regulated exchange run by QCX LLC, with its own order book and dollar funding by card, ACH or wire after KYC. It opened to everyone when the waitlist came off in May 2026, and it has grown fast: The Block has it at about $5.1 billion so far in September, ahead of the international book's $3.3 billion. We cover its background in our Polymarket US guide.

For arbitrage, it matters because it's the only other large, regulated US order book with a retail API (REST and WebSocket, 20 requests per second per key). Its taker fee has gone up twice since April. From September 25, 2026, takers pay 0.0695 × contracts × p × (1 − p), makers earn a 0.0125 rebate on the same curve, and high-volume takers get part of their fees back. The trade-offs are real. The books are thinner: one July comparison found a 50,000-contract order slipped 3.62 cents here against 0.05 cents on the international book. Orders not processed within five seconds are rejected, and a weekly maintenance window on Thursday mornings cancels every resting order. It also isn't live in every state, so check before you sign up.

4. SX Bet: A Sports Exchange for Non-US Traders

SX Bet is a peer-to-peer sports exchange licensed in Anjouan and settled in USDC. It offers REST and WebSocket APIs and makes a natural third venue for sports, but it's much smaller (about $48 million matched over the last 30 days, per DefiLlama) and unavailable in the US, UK, France, Germany, Spain, the Netherlands, Australia and Ontario. Check fees before you model a trade: its docs list a 1% taker fee on winning profit, while some of its announcements describe straight bets as fee-free. Live bets carry a 3 to 10 second delay, and postponed games are voided after 12 to 48 hours, which differs from Kalshi and Polymarket. More detail in our SX Bet arbitrage guide.

5. Predict.fun: A Crypto-Native Book on BNB Chain

Predict.fun is a BVI-registered prediction market settled in USDT on BNB Chain, with REST and WebSocket APIs. Takers pay 2% of the cheaper side's price (2% × min(p, 1 − p)), so fees stay small at extreme prices, and makers pay nothing. It traded roughly $300 million over the last 30 days and resolves through the UMA oracle, like Polymarket. It isn't available in the US, UK, France, Singapore and several other countries.

Why the Rest Rank Lower

Novig and ProphetX became CFTC-regulated exchanges in June 2026 and are growing fast in US sports. Novig's pregame straight bets are free for takers, and ProphetX charges 2% of net gains. But API access is gated: Novig opens it to approved liquidity providers (generally with a $30,000 minimum), and ProphetX by application. ProphetX's two-way soccer moneylines are also voided on a draw, while Kalshi and Polymarket list the draw as its own outcome, so those markets don't pair cleanly.

PredictIt is politics only, caps positions at $3,500 per contract, charges 10% of profits and bans automated trading. It's useful as a price signal, not as an arb leg.

Comparison Table

Why Most New Prediction Apps Don't Add New Arbitrage Venues

The number of places Americans can trade event contracts exploded in 2025 and 2026. The number of independent order books you can trade automatically did not.

Many apps are front-ends. Coinbase's prediction markets run on Kalshi's order book, so their prices are Kalshi's prices and there's nothing to arb between them. Robinhood routes event contracts to Kalshi, ForecastEx, Rothera (its exchange venture with Susquehanna) and OG.com, with no API for event contracts. Others run genuinely separate books: DraftKings Predictions trades on its own DKeX exchange plus CME and Crypto.com books, and FanDuel Predicts on CME and Crypto.com books. Separate books can disagree, but we couldn't find a retail trading API for either, and without one you can't act on a gap that lasts seconds.

A few are worth watching. Interactive Brokers runs ForecastEx and offers an API for it, Gemini's prediction markets have a public trading API, and Crypto.com's exchange has a retail API in preview for approved accounts. If any of them build real depth, they'll earn a place on this list.

The Best Pairs for Prediction Market Arbitrage

Since every arb has two legs, the useful question is which pair to run.

For US Traders: Kalshi and Polymarket US

Both are CFTC-regulated, both have retail APIs, and both list the major US sports, so this is the default US pair. Their taker fee curves are almost identical (0.07 against 0.0695), which means a gap has to clear two fees before it pays. The difference is on the maker side: Kalshi charges makers on many sports series, while Polymarket US pays them, so resting the Polymarket US leg can turn a marginal gap into a real one. Settlement lines up well on cancellations, since both use a last fair price, but postponement windows differ: 48 hours on Kalshi against about two weeks on Polymarket US.

That's why fee modeling and order type matter more than the headline gap. Use our arbitrage calculator for the stake split, then take fees off before you trust the margin.

Outside the US: Kalshi and the International Polymarket

This is the best-documented pair. A study published in January 2026, covering more than 100,000 events on 10 venues from 2018 to 2025, found that equivalent markets stayed 2 to 4 percent apart on average after execution costs, and that the gaps persisted. It also found that only about 6% of events were listed on more than one venue at the same time, which is why overlap matters so much. The pair is only open to you if you're located somewhere both venues allow. Both block the UK, France, Italy, Poland, Australia, Singapore, Taiwan and Thailand; Kalshi also excludes Canada, India, China and the UAE; and Polymarket also restricts Germany and Brazil. Kalshi's restrictions apply to where you are, not just where you live. For a deeper look at how these two venues price the same events, read our Kalshi vs Polymarket arbitrage guide.

Watch the settlement rules closely on this pair. A cancelled NFL game resolves 50-50 on Polymarket but at a last fair price on Kalshi. A cancelled soccer match resolves No on Polymarket. A postponed game stays open on Polymarket until it's played, while Kalshi settles after 48 hours. Any of these can turn a locked-in margin into a loss.

A Prediction Market Against a Sharp Sportsbook

The third route pairs a prediction market with a sharp book like Pinnacle. Sharp books set some of the most efficient sports prices, and prediction markets can lag them when news breaks, so the edge usually comes from trading the prediction market toward the sharp line. We cover the mechanics in cross-book arbitrage.

How Much Edge Is Actually There?

Less on the obvious markets than most arb marketing suggests. When we compared 26 upcoming NFL moneylines on Kalshi and Polymarket on September 25, 2026, mid-prices were never more than a cent apart, and the cheapest two-venue hedge cost $1.009 after Kalshi's taker fee, so there was no arb to take. Liquid pregame lines on the biggest venues are efficient.

The gaps show up elsewhere: in thinner markets, around breaking news, in live trading and on newer venues. Speed and size decide who gets them. A 2026 study of Polymarket NBA markets found single-market arbitrage windows were rare and lasted a median of 3.6 seconds, and most of the more common multi-market opportunities could only be filled for about 15 shares. At those speeds, manual arbitrage mostly means watching prices that are already gone.

Risks That Decide Whether an Arb Is Real

• Settlement mismatch. Different tie, postponement and cancellation rules can break a hedge that looked perfect. Read both contracts' rules before you trade a pair for the first time.
• Fees in the middle of the range. With p × (1 − p) fees on both legs, a 3-cent gap near 50 cents can be a loss.
• Legging risk. If one leg fills and the other doesn't, you hold an unhedged position, the naked leg problem. Order delays (Polymarket's live sports delay, SX Bet's 3 to 10 seconds on live bets, Polymarket US's five-second rejection rule) make it more likely.
• Thin books. The price you see may cover only a few hundred dollars. Size to the depth on both sides, not the top of the book.
• Access and regulation. State court rulings, national blocks and venue rule changes moved fast in 2026. Only trade where you're legally allowed to, and never use a VPN to get around a venue's restrictions: it breaks their terms and can get your balance frozen.

As with any trading, only put in money you can afford to lose.

How Claw Arbs Fits

Claw Arbs ships with 12 pre-installed venues, including the five prediction markets at the top of this list: Kalshi, Polymarket, Polymarket US, Predict.fun and SX Bet. Sharp books like Pinnacle (PS3838), BetInAsia and Sportmarket are in there too as price references. It watches every venue you connect at once, finds arbitrage and value across them, and executes both legs automatically in around 20 milliseconds.

You can see the kind of cross-venue gaps it tracks on the free live arbs board, and every membership starts with a 7-day free trial.

FAQ

What is the best prediction market for arbitrage?

Kalshi is the best anchor for most traders: it has the deepest regulated order book, a full API and a published fee formula. Arbitrage always needs a second venue, though. US traders usually pair Kalshi with Polymarket US, and traders in countries both venues allow pair Kalshi with the international Polymarket. SX Bet and Predict.fun add sports and crypto books for traders outside the US.

Can you arbitrage Kalshi and Polymarket?

Yes, if you can legally use both. US residents can't open new positions on the international Polymarket, but they can pair Kalshi with Polymarket US, a separate CFTC-regulated exchange. Outside the US it depends on where you are, since both venues restrict a list of countries. Before trading a pair, check that the two contracts settle the same way on ties, postponements and cancellations.

Is prediction market arbitrage risk-free?

No. An arb only locks in a return if both legs fill at the prices you expect and both contracts settle the same way. Fees near 50 cents, thin order books, one leg filling without the other, and different settlement rules on ties or cancellations can all turn a paper arb into a loss.

Do you need a bot to arbitrage prediction markets?

For most gaps, yes. Price differences on liquid markets can close within seconds (a 2026 study of Polymarket NBA markets measured a median of 3.6 seconds for single-market arbs), so you need API access and a live price feed to act in time. That is why venues without a retail API add little for arbitrage, however popular they are.

Bottom Line

The best prediction market for arbitrage in 2026 is really the best pair. Anchor on Kalshi for depth, a full API and published fees, then add the second venue your location allows: Polymarket US inside the US, the international Polymarket outside it, with SX Bet and Predict.fun as extra books for non-US traders. Model fees on both legs, read the settlement rules before your first trade on a pair, and size to the depth you can actually fill. The new wave of US prediction apps is worth watching, but until they offer real depth and a retail API, they won't change which venues arbers use.

Sources

• Kalshi fee schedule and Kalshi API docs
• Polymarket trading fees and geographic restrictions
• Polymarket US fee schedule
• SX Bet fees and Predict.fun fees and limits
• The Block, prediction market volume data
• Gebele and Matthes, Semantic Non-Fungibility and Violations of the Law of One Price in Prediction Markets (arXiv, January 2026)
• Cheng, Yang and Zou, Arbitrage Analysis in Polymarket NBA Markets (arXiv, April 2026)