World Cup knockout arbs held their pace but lost their depth

We measured earlier how long a single cross-venue gap stays open before the two books converge. That post looked at one 24-hour window across every sport on the feed. This one narrows to a single tournament and a specific kind of opportunity: a three-leg arb, where the three outcomes of a 90-minute soccer moneyline (home, away, draw) can be bought across Kalshi and Polymarket for less than a dollar combined. When that happens, the edge is the discount below a dollar, expressed as a percent of the combined cost, and the stake is sized to whichever leg has the thinner order book.

We pulled every confirmed three-leg arb from the World Cup knockout rounds and split it by round. The result is a clean pattern: the market kept tearing at roughly the same rate, but each tear got shallower and healed faster.

Round aggregates

Round	Games	Arbs	Pooled median edge	Pooled avg edge	Max edge	Median lifetime
Round of 16	8	48	2.81%	5.08%	28.53%	10.5s
Quarterfinals	4	29	1.21%	2.78%	14.53%	4.3s

Arbs per game barely moved: 8.0 in the round of 16 (48 arbs across the 6 of 8 matches that produced any), 7.25 in the quarterfinals (29 across all 4). Whatever drives a gap wide enough to become a fireable arb was still happening just as often. What changed is what happened once it opened. The pooled median edge fell by more than half, from 2.81% to 1.21%, and the pooled median lifetime fell by more than half again, from 10.5 seconds to 4.3 seconds. The two books were still disagreeing about as frequently. They were disagreeing by less, and fixing it faster.

Per-match view

Match	Round	Arbs	Median edge	Median lifetime	Max edge
Canada vs Morocco	R16	0	n/a	n/a	n/a
Paraguay vs France	R16	0	n/a	n/a	n/a
Brazil vs Norway	R16	5	8.00%	28.1s	16.49%
Mexico vs England	R16	16	1.94%	16.8s	8.79%
Portugal vs Spain	R16	3	3.44%	30.7s	8.97%
USA vs Belgium	R16	5	2.07%	52.7s	18.99%
Argentina vs Egypt	R16	16	3.18%	6.7s	28.53%
Switzerland vs Colombia	R16	3	1.12%	3.3s	20.32%
France vs Morocco	QF	8	1.87%	4.6s	7.09%
Spain vs Belgium	QF	3	0.92%	2.4s	1.21%
Argentina vs Switzerland	QF	5	9.57%	9.8s	14.53%
Norway vs England	QF	13	1.14%	4.8s	2.57%

Two matches sit outside the trend, and they're the same team both times. Argentina vs Egypt in the round of 16 carried the round's largest edge, 28.53%. Argentina vs Switzerland in the quarterfinals carried that round's largest edge too, 14.53%, along with a median edge that ran well above every other quarterfinal match. Nothing in our data explains why. One plausible reading is that the tournament favorite pulls in more casual order flow on both books, and casual flow moves faster and less carefully than the flow behind quieter matchups, leaving wider and more frequent gaps for the matcher to catch. Treat it as a reading of the pattern rather than a finding confirmed by price data alone.

What this doesn't show

Coverage of the opportunity engine began with the knockout rounds. Group-stage games were matched on both books, but the engine wasn't yet watching for arbs during that stage, so there's no group-stage baseline to compare against. Twelve games is a small sample for any round-over-round claim, and a single unusual match, in either direction, can move the pooled numbers more than the underlying pattern would suggest. The Argentina vs Switzerland quarterfinal was still open at the snapshot time behind these numbers, 2026-07-12 02:15 UTC, so its arb count and edges can still change as the game continues to trade.

None of this reads as an opportunity to go execute. A 4.3-second median lifetime describes how fast a public pricing gap corrects itself. It is far too short for a person watching two browser tabs to place both legs. Most of these edges, especially in the quarterfinals, closed before anyone could act on them.

A note on what's counted here. These are three-way soccer markets, and the matcher holds nearly all of them in a manual review lane for a disclosed settlement caveat: typically that one venue states how it settles a cancelled or abandoned game while the other stays silent, so the two books could in principle pay out differently in that tail case. The outcome match itself is confirmed, which is what puts a pair in the numbers above. The settlement caveat is a separate, per-market disclosure about that cancellation tail, and it's worth checking before treating any single pair as fully resolved.

The matched feed and the open gaps are on REST, free to read on any plan. Real-time push, where each new arb reaches you the instant it fires, is on Basic and Pro. The Quickstart pulls your first feed on a free key.