Cross-venue arbitrage
The gap you can see is almost never the gap you can keep. Every figure here is priced by walking both order books to 500 contracts and netting off taker fees on both legs plus settlement basis.
Will J.D. Vance win the 2028 Republican presidential nomination?
| Contract | Buy | Sell | Gross | Friction | Net edge | Size | Ann. | Closes |
|---|---|---|---|---|---|---|---|---|
Will J.D. Vance win the 2028 Republican presidential nomination? match 87% | 0.4400 Kalshi | 0.4770 Polymarket | +3.70pp | −1.81pp | +1.89pp | 500 | 2% | 801.4d |
Will Gavin Newsom win the 2028 Democratic presidential nomination? match 89% | 0.1300 Kalshi | 0.1480 Polymarket | +1.80pp | −0.87pp | +0.93pp | 500 | 3% | 801.4d |
Will Ted Cruz win the 2028 Republican presidential nomination? match 89% | 0.0100 Polymarket | 0.0130 Kalshi | +0.30pp | −0.17pp | +0.13pp | 500 | 6% | 801.4d |
Will Ivanka Trump win the 2028 Republican presidential nomination? match 89% | 0.0090 Polymarket | 0.0100 Kalshi | +0.10pp | −0.15pp | −0.05pp | 500 | — | 801.4d |
Will Nikki Haley win the 2028 Republican presidential nomination? match 89% | 0.0040 Polymarket | 0.0030 Kalshi | −0.10pp | −0.10pp | −0.20pp | 500 | — | 801.4d |
Will Cory Booker win the 2028 Democratic presidential nomination? match 89% | 0.0060 Polymarket | 0.0050 Kalshi | −0.10pp | −0.12pp | −0.22pp | 500 | — | 801.4d |
Will Pete Buttigieg win the 2028 Democratic presidential nomination? match 89% | 0.0530 Polymarket | 0.0530 Kalshi | +0.00pp | −0.43pp | −0.43pp | 500 | — | 801.4d |
Will Kamala Harris win the 2028 Democratic presidential nomination? match 89% | 0.0842 Polymarket | 0.0855 Kalshi | +0.13pp | −0.63pp | −0.50pp | 500 | — | 801.4d |
Will Marco Rubio win the 2028 Republican presidential nomination? match 89% | 0.1770 Polymarket | 0.1800 Kalshi | +0.30pp | −1.11pp | −0.81pp | 500 | — | 801.4d |
Why these rows and not more
Only pairs scoring 0.8 or above are priced. That gate is set from measurement, not caution. Pricing 24 pairs against live books produced a sharp boundary: every pair at 87% or above was genuine, and every pair at 75% or below compared structurally different questions — a Polymarket contract on winning the 2028 presidential election against a Kalshi contract on winning the Democratic nomination, or winning a Brazilian election against merely advancing in it.
Those false pairs showed roughly twice the apparent spread of the genuine ones — mean gross 1.22pp against 0.64pp — because comparing two different events manufactures edge out of nothing. In an arbitrage surface that is the dangerous failure, not the harmless one: it prints money that was never there. At most 24 pairs are priced per pass, ranked by match confidence.
What friction covers
Kalshi
as of 2026-08-28Taker fee = ceil(0.07 x contracts x P x (1-P)) in cents. Peaks at P=0.50 (1.75c per contract) and falls to near zero at the tails.
Polymarket
as of 2026-08-28No percentage trading fee on binary CLOB markets. Gas is relayed and not charged per fill. Settlement is USDC, which carries basis against USD.
Plus 0.08pp of USDC/USD settlement basis: Kalshi settles in dollars and Polymarket in USDC, so a cross-venue position carries peg exposure for its whole life. The quadratic in Kalshi's fee is what makes this surface counter-intuitive — it peaks at even money and collapses at the tails, so an identical gap is worth very different amounts depending on where the contract trades.
A displayed edge is not an executable order. These are prices that existed at a size at a moment; whether your order reaches the book before someone else takes it is not modelled, and the latency between this poll and your fill is frequently larger than the edge.