Tennis 2026 — season books and the clay record

Every tennis book on this page has its deepest flow on a longshot.

The ATP Grand Slam book turned $9,934 yesterday and $6,177 of it—62%—went through Frances Tiafoe at 1.5%. Ben Shelton at 12.5% and Novak Djokovic at 11.5%, the two live favourites, took $740 and $378 between them. On the WTA side, Iga Swiatek at 19% took $1,091 of a $1,697 book, which is the same shape with a shorter price.

The ATP #1 ranking book is the sharpest version of it. Jannik Sinner is 84%, Alexander Zverev 12%, Carlos Alcaraz 7%—and the open interest runs exactly backwards: $4,981 on Alcaraz, $4,666 on Zverev, $3,754 on Sinner. The 84% favourite carries the least money in his own book, and Zverev outtraded him yesterday $2,234 to $1,634.

One structural note that explains part of it: Sinner's Grand Slam contract is already settled—he won one—and it still shows as the deepest leg at $38,869 of open interest, quoted at a no-quote 50%. Roughly half the "open interest" in that book is a resolved position waiting to be paid.

Roland-Garros is the settled record this page was built on; the season complex below is what is still live.

The clay record. Alexander Zverev and Mirra Andreeva won Roland-Garros. Kalshi purged its own French Open series after settlement; Polymarket kept both books, which is why the record survives here at all.

This is a recurring asymmetry worth knowing: Kalshi delists settled tournament series aggressively, Polymarket does not. If you want a market's post-mortem, Polymarket is usually the exchange that still has it.

The 2026 season books, which run to December 31.

ATP Grand Slam ($9,934): sums to roughly 91.5% across live legs. Sinner's leg is settled and inflates the open-interest picture. Among live contracts, Shelton leads at 12.5%, Djokovic at 11.5%, Fritz at 6%—and Tiafoe at 1.5% is taking most of the flow.

WTA Grand Slam ($1,697): Sabalenka 25.5%, Swiatek 19%, Gauff 16.5%. Open interest is more evenly distributed here than on the men's side—$8,008 on Swiatek, $7,088 on Sabalenka, $4,077 on Gauff—and roughly tracks the prices, which the ATP book does not.

The two contracts below are the ones carrying the flow: Tiafoe's 1.5% leg and Swiatek's 19%.

• Whether Tiafoe's 1.5% leg keeps taking the book. Sixty-two percent of daily volume on a contract priced at one-in-sixty-six is either an accumulation or a market maker. Two more days of it and the price should start to move.
• The ranking book's inversion. Zverev outtrading Sinner four months out is the closest thing to a directional signal in season-long tennis right now.
• The US Open, which is not on this page. Kalshi's men's draw runs $1.26M a day and Polymarket's runs $860k; both live in the dedicated US Open workspace rather than here.
• How much of the ATP Grand Slam open interest is dead. Sinner's settled leg is $38,869 of the book's total. Any comparison of "open interest by player" in that book is misleading until it pays out.
• Whether Kalshi relists a WTA year-end ranking book. There is an ATP one and no women's equivalent, which is the most obvious gap in the season complex.

The year-end #1 ranking, and its inverted open interest.

Sinner 84% / Zverev 12% / Alcaraz 7%, summing to 103.5%—so read the levels as slightly rich across the board. The interesting part is underneath: the two contracts the book says are unlikely carry $9,647 between them against the favourite's $3,754.

There is a benign explanation—holding the favourite at 84 cents ties up a lot of capital for 16 cents of upside, so open interest naturally concentrates in cheaper legs. But the volume inversion is harder to wave away: Zverev at 12% outtraded Sinner at 84% by more than a third yesterday, four months from settlement.

The settled record, and a rendering note.

Cincinnati has finished and its book shows every player at a 50% midpoint—the platform's standard display for a Categorical that has settled between quote refreshes. The $108,987 attached to it was traded during the tournament. The same artifact appears on Sinner's settled Grand Slam contract, and on any recently-resolved Categorical on the exchange. It is not a field of coin flips.