Both Sides, Bought for Less Than $1
Sometimes Kalshi and Polymarket price the same event so that both sides together cost less than the $1 the winner pays. Arbitrage automation finds those gaps and buys both sides at once, so one side pays $1 whichever side wins.
Where It Stands Today
Arbitrage automation is in paper testing. It runs all day, every day, and records every basket it would buy at the prices it could have bought, but it sends no real orders. Live trading is off for every account. It opens to members only after the paper result is positive.
Simulation mode records what it would buy. No order reaches a venue.
Two prediction markets with deep order books. No sportsbooks.
It trades international Polymarket, which does not accept US connections.
What an Arbitrage Is
One Match, Two Prices
A tennis match is listed on both venues. Each side of it pays $1 if it wins and nothing if it loses. When the two venues disagree enough, you can buy one player on Kalshi and the other player on Polymarket for less than $1 in total:
| Leg | Price |
|---|---|
| Kalshi: Player A wins | 55¢ |
| Polymarket: Player B wins | 42¢ |
| Both sides together | 97¢ |
| Paid out, whichever player wins | $1.00 |
| Gap before fees | 3¢ per pair |
Fees come out of the gap. The automation counts both venues' fees, at the most each order could cost, before it buys anything. If the gap does not survive fees and your minimum return, there is no basket.
Three Kinds of Basket
Same Question, Two Venues
An event such as an economic decision, listed on both Kalshi and Polymarket. A pair is added only after a person has read both venues' rules and confirmed they settle the same way.
Same Match, Two Venues
Tennis, esports and other matches listed on both venues. The players or teams, the competition and the scheduled start must all agree. Matching names alone is never enough.
All-Outcome Baskets
A Polymarket event where only one outcome can win. Buying “No” on every outcome means all but one of them pay, whichever outcome wins.
How a Basket Gets Bought
Scan both venues
Every 60 seconds it reads Kalshi and Polymarket for gaps, all day, whether or not anyone has a browser open.
Prove it is the same event
Both legs must be about the same event: the same players or teams, the same competition and the same start time. When anything is unclear, the pair is dropped.
Size the basket
Every leg gets the same number of contracts, so one of them pays out whatever happens. One budget covers the whole basket, fees included. Each contract is priced at its order limit, not the average, and it uses at most half of the shares on offer.
Check the prices again
Just before sending, it reads fresh order books. A price older than five seconds is never sent.
Send every leg at once
Each leg is one exact-size, fill-or-kill order: it fills completely at your limit or not at all. All legs go out together.
Wait for both venues to settle
The money stays on both venues until each one settles. The result is booked only from the venues' own settlement.
The Void-Safe Rule
When a Match Is Called Off
A called-off match is the biggest risk in same-match baskets. Polymarket then pays 50¢ on each side, and Kalshi pays its own “fair price”. The two legs no longer add up to $1, and both can lose.
| The rule | What it does |
|---|---|
| Polymarket leg below 48¢ | A same-match basket buys its Polymarket side only below 48¢. If the match is called off, that side’s 50¢ payout still covers what it cost. |
| 48–52¢ stays out | This is where a called-off match’s Polymarket price drifts, which can look like a gap when it is not one. |
| Kalshi side | Kalshi’s fair price on a called-off match can still move. The rule cuts most of the risk, not all of it. |
Why it exists: in our paper records, 70 of 301 settled same-match baskets were called off, and those turned a small gain into a loss. Under this rule, 1 of 80 was called off. The rule skips most same-match baskets. That is the price of not losing on both sides.
When Only One Side Fills
Fill-or-kill applies to each order, not to the basket. Two venues cannot fill as one, so one side can fill while the other misses. This is what happens then:
- It tries one sell-back of each side that filled, using the shares actually bought and the bids on offer right then, within the unwind loss budget you set.
- If the sell-back cannot finish within that budget, the basket shows needs attention with the shares still held. You manage that position on the venue. There is no button that hides it.
- An order whose result is unknown is never sent again. It asks the venue for that order by its original ID until the answer is certain.
- While any basket is unresolved, your account takes no new entries, for arbitrage or for model picks.
Your Controls
Set Your Own Limits
Open Automation in your account and choose Arbitrage. Pick a mode: Simulation records baskets with no orders; Live will use your connected accounts once live trading opens. Then set your limits:
| Setting | Default | Most allowed |
|---|---|---|
| Total per position (all legs together) | $25 | $100 |
| Daily spending cap | $100 | $1,000 |
| Maximum open positions | 3 | 20 |
| Minimum net return | 0.5% | — |
| Unwind loss budget | $2 | $10 |
Stop new entries any time. Open positions keep being watched until they settle. Your ordinary auto-trade limits apply too, and the tighter limit wins.
What Live Mode Will Need
Your own Kalshi account with an API key that has Read all data, Trade and Transfers, plus the Polymarket automation wallet. Transfers lets it move your Kalshi cash to the part of Kalshi that holds the market before it signs an order.
Both accounts must be armed in Automation, with an active subscription and your explicit consent to automatic trades and sell-backs.
Where It Works
Arbitrage uses international Polymarket, which does not accept US connections, so it is not available in the US yet. Polymarket US and sportsbooks are not supported.
Location checks run before live orders, the same as for Auto-Trade.
What Can Still Go Wrong
Arbitrage Is Not Risk-Free
- Settlement rules can differ. A same-match return assumes the match is played normally; a cancellation, walkover or postponement can be settled differently on each venue.
- Prices move within about a second. In early paper testing, about one recheck in seven found a side gone. A sell-back costs the spread.
- Your money is locked until both venues settle, sometimes for days.
- Gaps are small and shared. When other members have just bought the same gap, your position can be smaller or skipped.
- Paper results do not prove that real orders would fill. Live results will be reported apart from paper.
Open the Arbitrage Screener
Every live Kalshi and Polymarket gap, what both sides cost, and the paper record.
Read the Auto-Trade Guide
Connecting your accounts, arming them, and the limits shared with model-pick trading.
One Paper Record, Graded at Real Payouts
A paper basket is graded only when every leg has a confirmed settlement from its venue, and called-off matches are graded at what the venues actually paid. The record restarted on October 6, 2026, when the void-safe rule began. Older entries are archived: they still settle, and they are kept apart from the new record.
Full Access
- Less than $1 a day — one winning pick can pay for months of access
- +111 units of tracked profit — that's +$11,100 at $100/unit, verified in public
- Zero research needed — the exact pick, odds, and bet size handed to you every day
- Everything included — every sport, every model, every market. No tiers, no upsells