S&P 500 (SPX) Opens Up or Down on August 17?
No meaningful repricing — the probability is steady.
The pricing is supported by healthy trading volume and market depth, a tight spread.
How credible was the move?
Three separate questions — a move can be genuine while the latest price is still settling. Methodology →
Move validity
Is the move backed by real trading and depth?
StrongThe pricing is supported by healthy trading volume and market depth, a tight spread.
Consensus stability
Has the market settled at the new probability?
StableThe probability has held near its current level over the past several hours.
Contract clarity
Will the rules resolve without ambiguity?
HighThe resolution rules are relatively specific, with a named source and a defined deadline.
From the latest trade tape (most recent 200 prints) — a live activity sample, not a lifetime total.
What this market actually measures
This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on August 17 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day. This market will resolve to "Down" if the official S&P 500 Index open price for S&P 500 (SPX) on August 17 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day.
This summary shows the opening of the venue's official rules. ProbCast has not yet generated an independent plain-English interpretation for this contract — review the full rules before relying on it.
View full official resolution rules
This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on August 17 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day. This market will resolve to "Down" if the official S&P 500 Index open price for S&P 500 (SPX) on August 17 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day. E.g., ordinarily, a market on Monday would refer to the previous Friday for its most recent closing price, unless that Friday were a market holiday, in which case it would refer to Thursday, or the next most recent trading day. If the two prices are exactly equal, this market will resolve 50-50. Note that all figures will be rounded to the nearest cent using standard rounding. If SPX does not trade at all during the regular session, the market will resolve 50-50. If either of the relevant days are shortened (for example, due to a market holiday schedule), the official open/close price published by S&P 500 Index for that shortened session will still be used for resolution. If the previous trading day has no official closing price (for example, due to a trading halt into the market close, system issue, delisting, or other disruption), the market will use the last valid on-exchange trade price of the regular session as the effective closing price. The resolution source for this market is the Wall Street Journal, specifically the Open/Close values published by the WSJ under "Historical Prices". US: https://www.wsj.com/market-data/stocks EMEA: https://www.wsj.com/market-data/stocks/emea ASIA: https://www.wsj.com/market-data/stocks/asia
What could move this market next?
- The market's deadline arrivesAugust 17, 2026 at 4:00 PM ET
The contract must resolve based on what has happened by this date.
- Confirmation at the resolution source (wsj.com)
The rules name this source as the basis for settlement.
Derived from the contract's own mechanics as of Aug 17, 1:07 PM ET. ProbCast does not list scheduled meetings, announcements, or data releases it cannot verify.
Advanced analysis (experimental)
Research signals — these models are still accumulating the history needed for full validation, and they can disagree with the headline read. Model confidence: high · expected error ±11 pts.
What's happening
Near resolution or with ambiguous wording, pricing is mechanically thin and can swing on tiny trades. Read end-of-life prices with extra caution.