US Index Markets 2026

Kalshi delisted its daily index books, and what replaced them has almost stopped trading. Polymarket's "S&P 500 (SPY) closes above ___ on September 11" is the single next-session index contract listed anywhere on this platform, and it turns $597 across eleven strikes—down from roughly $3,000 a session ago and $18,500 the session before that. $735 is 96.1%, $750 is 94.5%, $765 is 7.5%, $780 is 3.85%, which brackets a close somewhere in the mid-750s but with almost nothing behind the quotes.

Its busiest rung is the one it prices at half a cent. "$785" is 0.55% and took $502 of a $597 board—84% of the day's flow on the strike furthest out of the money. That is the same shape this platform shows in crypto, in weather and in energy: the money goes to the cheap tail, not to the strike nearest the money.

Against that, the year-end boards are enormous. Kalshi's 2026 S&P year-high ladder, the year-low ladder, and the December 31 close boards for the S&P and the Nasdaq 100 carry the open interest the daily books used to churn against, and they barely move day to day. Their crash buckets—S&P above 4,000, Nasdaq 100 above 19,000—remain the most-traded legs on their ladders.

Polymarket's September SPY touch board is the middle ground: a month-long horizon with real depth, asking what the index touches rather than where it closes.

What is still missing is a same-session book on a second exchange. Until Kalshi relists one, this page cannot show the cross-exchange index spread it exists to show.

Polymarket's September 11 SPY board turns $597 across eleven strikes and settles at 20:00 UTC tomorrow. $735 is 96.1%; $750 is 94.5%; $765 is 7.5%; $785 is 0.55% and holds $502—84% of the board on its furthest-out strike.

Beside it, the September touch board, which is where the month's real index flow sits. There is no Kalshi counterpart to either.

The realized-extreme ladders are the other side of the same position: where the year-end boards ask where the index finishes, these ask how far it travels. They carry a fraction of the year-end open interest and are the only index contracts on Kalshi whose distribution has moved this week.

Nasdaq, 18,999.99 or below: 3.5%, $1,105,059 of open interest, $1,156 of volume—the deepest single position and the busiest contract on a thirty-rung board. That strike implies roughly a 40% fall from here by December 31.

S&P, 6,200–6,399.99: 0.5%, $148,279 held, and $4,003 traded today—13% of the whole event's day. 5,800–5,999.99 at 0.5% took another $1,666.

Between them the two crash buckets took $5,669 of a $37,017 combined day. On boards this positional, the daily volume is almost entirely people adding to disaster hedges.

Polymarket's December S&P board and Manifold's end-of-2026 threshold question, next to Kalshi's own year-end ladders. Polymarket has consistently priced S&P touches richer than Kalshi prices finishes—a touch-versus-close distinction that is easy to read as a spread and is not one.

Polymarket's next-session board settles at 20:00 UTC tomorrow. The year boards settle January 1.

• Whether Kalshi relists a daily index book. Until it does, this workspace cannot show a same-session cross-exchange index spread, which is the comparison it exists to make.
• The collapse in next-session depth: roughly $18,500 to $3,000 to $597 across three sessions, with the index barely moving. A book thinning out that fast usually means the flow found somewhere else to go, not that the question got easier.
• The $785 rung at 0.55% holding $502. A near-worthless strike taking most of a thin board is the retail signature, and it shows up here as clearly as anywhere.
• The crash buckets on the December 31 boards. They are still the busiest legs on those ladders, and they are the cheapest.
• The year-high and year-low chains as the actual home of index conviction on this platform. Daily flow is noise against their open interest.