Kalshi vs Polymarket vs Sportsbooks: World Series Game 1 Odds Data (2026)

Kalshi and Polymarket priced Game 1 of the 2026 World Series almost exactly like the sharpest sportsbook. At first pitch on 23 October, Polymarket had the Milwaukee Brewers at 63.5¢, Kalshi's quotes implied 62.6% once its fee is stripped out, and Pinnacle's no-vig line said 63.3%. Milwaukee won 3–2 over the Tampa Bay Rays, and that one win moved its World Series odds about 10 points on both prediction markets.

The numbers come from the OddsFantasy scanner, which read Game 1 prices from 13 venues 6,449 times between 20 October and first pitch, plus Kalshi's and Polymarket's public market data. Here is what each venue charged, where the price gaps were, and how the money moved once the game started.

Key numbers

• Fair win probability for Milwaukee at first pitch: Pinnacle 63.3%, Polymarket 63.5%, Kalshi 62.6%. The 10 other sportsbooks and exchanges in the scan ranged from 61.3% to 65.1%.
• Cost of betting both sides: 2.14% at Pinnacle, 2.32% in Polymarket taker fees before the spread, and 3.26% on Kalshi with its fees. The other sportsbooks charged 2.03% to 7.15%.
• Moneyline arbitrage: 4 small gaps in the week before the game, the largest 0.41%. At first pitch there was none: the best prices across all venues added up to 100.8%.
• 58 distinct arbitrage opportunities in total, almost all on run lines and totals. 15 of the 18 worth 1% or more opened in one 45-minute window on 22 October.
• Kalshi traded 26.1 million contracts on the Game 1 winner, 62.5% of them after first pitch. Its busiest minute was 11:21 p.m. ET in the ninth: 421,285 contracts on a double play that was later overturned.
• Series odds after Game 1: Polymarket 64.2% to 74.0%, Kalshi 62¢ to 73¢.

How each venue priced Game 1

Every venue agreed to within a few points. The fair figure removes each venue's margin in proportion to its prices, so it shows the probability a price implies once the house edge, fee or commission is taken out. The margin is what a bettor pays for the bet: how far the cost of backing both teams goes over the $1 payout.

• Pinnacle: Brewers 1.546, Rays 2.670. Margin 2.14%, Brewers fair 63.3%.
• Polymarket: Brewers 63.5¢, Rays 36.5¢ at the mid price. The sports taker fee is 1.16¢ a share on either side, 2.32% for both, plus the bid-ask spread. Brewers fair 63.5%.
• Kalshi: 63¢ to back the Brewers and 37¢ to back the Rays at the best quotes, plus a 1.6¢ taker fee on each. Margin 3.26%, Brewers fair 62.6%.
• Two betting exchanges, after commission: margins of 2.50% and 3.34%, Brewers fair 62.7% and 62.9%.
• Eight other sportsbooks (offshore, crypto, Asian and African): margins from 2.03% to 7.15%, Brewers fair from 61.3% to 65.1%. Seven of the eight sat between 61.3% and 63.1%.

Prediction-market fees are charged on p × (1 − p), so they are highest on coin flips and shrink toward 0¢ and 100¢. On a 64¢ Kalshi contract the taker fee is 1.61¢, or 2.52% of the stake. On a 63.5¢ Polymarket share the sports taker fee is 1.16¢, or 1.82%. The Kalshi and Polymarket fee calculator works it out for any price and size.

The price drifted toward Milwaukee all week

When the Game 1 markets opened on 20 October, Pinnacle's fair line had Milwaukee at 59.6%, Polymarket at 59.5¢ and Kalshi at 61¢. By first pitch all three had moved about 4 points toward the Brewers. The prediction markets tracked the sharp line the whole way: in 60 hourly readings Polymarket was never more than 1.4 points from Pinnacle, and the average gap was 0.3 points.

The sharpest move came between 4:22 and 4:38 p.m. ET on 22 October, when Pinnacle moved Milwaukee from 59.5% to 61.3% and shifted its run totals toward the over. Every venue followed, but not at the same speed, and that is where the week's best arbitrage came from.

Where the arbitrage was, and wasn't

An arbitrage is a pair of prices on different venues that together cost less than the payout, after fees and commission, so backing both sides locks in a return. Before first pitch the OddsFantasy scanner found 58 distinct ones on Game 1. The median was worth 0.35% of the stake. The best was 2.76%, on over/under 6.5 runs, Pinnacle against an offshore sportsbook on 22 October.

The moneyline, where most of the money goes, was close to airtight: 4 gaps all week and none above 0.41%. The other 54 were on the run line and other handicaps (24), the game total (22) and Tampa Bay's team total (8), the markets that venues update less often.

Polymarket produced exactly one gap after its fee, worth 0.01%. Kalshi was on one side of 18, up to 2.14%.

The 45-minute window on 22 October

15 of the 18 gaps worth 1% or more opened between 4:20 and 5:05 p.m. ET on 22 October, as the market repriced. Kalshi moved its moneyline and total in the same quarter-hour, but its Milwaukee −1.5 run line stayed at 2.51, fee included, until about 4:57 p.m. Against a sportsbook's Tampa Bay +1.5, that was a 1.7% gap after Kalshi's fee.

That is the pattern to know. On a game this liquid, arbitrage rarely comes from one venue being wrong for long. It comes from news: the sharp line moves and a slower venue hasn't followed yet. The OddsFantasy arbitrage scanner is built to catch those minutes, with fees already taken off. For the full method, see how Polymarket and Kalshi arbitrage works.

Value bets

The value-bet scanner compares every price with Pinnacle's no-vig line and lists the ones that beat it. On Game 1 it flagged 17 distinct prices, with a median expected value of 1.87% and a range of 1.32% to 4.04%. The most persistent was an offshore sportsbook's Tampa Bay team total under 3.5 and under 2.5 runs, listed 98 times between 20 and 23 October. Kalshi beat the sharp line three times: the Rays moneyline at 1.87%, and the game total under 7.5 and under 5.5 runs. The +EV scanner shows these live.

Most Kalshi trading happened during the game

Kalshi's two Game 1 winner markets traded 26.1 million contracts: 13.1 million on Milwaukee and 13.0 million on Tampa Bay, each paying $1. 62.5% of them traded after 8 p.m. ET. The split was lopsided: 40% of the Milwaukee contracts traded during the game, against 85% of the Tampa Bay ones, as the Rays became the cheaper side.

Polymarket reported $1.91 million of volume across its Game 1 markets, $1.23 million of it on the winner. The two venues count volume differently, so compare each with itself rather than with the other.

During the game the two prediction markets moved together, minute by minute. Their prices for Milwaukee were within 1 point of each other in 92% of the minutes. The Brewers went from 63.5¢ to 85.5¢ on Polymarket after scoring twice in the first inning, fell to 68.5¢ by 9:35 p.m. ET, and reached 97¢ going into the ninth.

Then the ninth swung both markets hard. With the Rays threatening, Milwaukee fell to 77¢ by 11:20 p.m. Kalshi jumped to 99.5¢ a minute later on what looked like a game-ending double play: its busiest minute of the night, with 421,285 contracts traded. The call was overturned, a run scored to make it 3–2, and Milwaukee fell back to 82¢ on both venues before a strikeout with the tying run on third ended the game at 11:27 p.m.

What one win did to the series

Before Game 1, Polymarket's World Series market had Milwaukee at 64.2% and Kalshi's series market had the Brewers at 62¢. By the next morning they read 74.0% and 73¢. One win was worth about 10 points of title probability. Polymarket's 2026 World Series champion market has traded $45.8 million since it opened.

Game 2 board

Game 2 is in Milwaukee on 24 October at 8 p.m. ET. At 8:20 a.m. ET that morning every venue had the Brewers between 53.0% and 54.0%. Pinnacle priced them at 1.813 against 2.13 for the Rays, a 54.0% fair price with a 2.11% margin. Kalshi's fee-inclusive prices implied 53.4% with a 2.72% margin, and Polymarket had the Brewers at 53.5¢.

Method

• Venues: 13 in the OddsFantasy scanner (Pinnacle, Kalshi, two betting exchanges and nine sportsbooks; 6,449 price snapshots, 20–24 October 2026), plus Polymarket's public price history. One sportsbook's last pre-game price was a day old, so it is left out of the first-pitch board.
• Kalshi at first pitch: the best quotes from Kalshi's minute candlesticks. Backing a team costs the lower of its Yes ask and the other team's No ask.
• Fees: Kalshi's taker fee of 0.07 × p × (1 − p) a contract, rounded up; Polymarket's sports taker fee of 0.05 × p × (1 − p); exchange prices net of commission.
• Fair probability: each venue's two moneyline prices with the margin removed in proportion.
• Arbitrage and value counts: distinct opportunities (market, sides and venues) listed before first pitch, fees included. 240 listings from one Asian sportsbook dated before 10:05 a.m. UTC on 20 October are excluded: until a fix that morning, its series prices were being read as game prices.
• Times are Eastern (ET) unless marked UTC.

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