S&P 500 (SPX) Opens Up or Down on June 1?

Platform comparison

Market context

The S&P 500 will open on 1 June 2026 either above or below the prior trading day's close. This is a binary gap trade: the market settles "Up" if the official opening price exceeds the previous session's closing level, and "Down" if it opens lower. The settlement window closes at 20:00 UTC on that date, giving traders the full US market session to confirm the official open against the prior close (likely 31 May, unless that Friday is a holiday, in which case 29 May applies). On Polymarket, this contract currently trades at 100% implied probability for "Up," suggesting the crowd expects a gap higher with near-certainty—a positioning that warrants scrutiny given overnight gaps occur in both directions with material frequency.

Historical data on S&P 500 opening gaps shows roughly 50–55% of sessions open higher than the prior close, with the remainder opening lower. The 100% crowd probability here reflects either an extreme skew in market sentiment or a technical artefact of low liquidity in this particular contract. Gap direction depends on overnight news flow, futures price action (ES contracts trade 23 hours daily), and broader sentiment shifts between US market close and open. A 100% reading is statistically inconsistent with actual market behaviour and suggests either very few traders have committed capital to this market or there is a structural imbalance in order flow on Polygon.

Watch for major economic data releases scheduled between market close on 31 May and the 1 June open—employment figures, manufacturing surveys, or Federal Reserve communications can drive significant overnight moves in ES futures. Earnings announcements from large-cap constituents, geopolitical developments, or shifts in Treasury yields overnight will influence gap direction. The conditional token mechanics on Polygon mean settlement is deterministic once the official S&P 500 opening price is published; traders should verify the data source used by Polymarket's oracle before committing USDC.

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to Polymarket UK, which mirrors the Polymarket order book directly.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Is this market available outside the US?

Polymarket UK is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

What does it cost to trade on Polymarket UK?

Zero. Polymarket UK routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, Polymarket UK triggers a quick verification flow that finishes in minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.