The S&P 500 ended June on a high note, wrapping up its best quarter since 2020. But if you ask the crowd on Polymarket, the benchmark index might stumble out of the gate for the second half of the year.

On Tuesday, the S&P 500 gained 0.79% to close at 7,499.36. Yet the July 1 Polymarket contract implies just a 27% probability that the index will open higher on Wednesday. That's a pretty bearish signal from a prediction market that's been known to get things right.

Why That Number Matters

Tuesday wasn't just any day—it marked the end of June, the second quarter, and the first half of 2026. The S&P 500 finished the first six months up 9.6% and posted a 14.9% gain in the second quarter, its strongest quarterly performance since the second quarter of 2020. Not bad for a market that's been navigating rate uncertainty and geopolitical noise.

But here's the thing: the S&P 500 only opened above 7,600 once in June—at 7,605.31 on June 3. A sharp technology-led pullback later in the month erased those gains before stocks recovered into quarter-end. Tuesday's close left the index just shy of that early-month peak, suggesting the rally might be running out of steam.

Investors are now turning their attention to fresh economic data. Wednesday brings the ADP employment report and the ISM manufacturing survey, plus remarks from Federal Reserve Chairman Kevin Warsh. All of these could offer clues on where interest rates are headed in the second half of the year.

The Countercase

Despite the cautious Polymarket bet, the market enters the second half with serious momentum. AI and semiconductor stocks have been on a tear, and chipmakers led Tuesday's advance. Nvidia (NVDA), Advanced Micro Devices (AMD), and Intel (INTC) all climbed, while the VanEck Semiconductor ETF (SMH) jumped more than 3%.

Beyond Wednesday's data, the big event is Thursday's June jobs report. A stronger labor market could cement expectations that the Fed will keep its restrictive policy stance, which would put fresh pressure on both equities and Treasury markets. S&P 500 futures were modestly lower early Wednesday, slipping 0.38%.

How The Previous Bet Played Out: The S&P 500 opened Tuesday at 7,441.27, above Monday's close of 7,440.43, meaning the June 30 Polymarket bet resolved "Up." The contract saw about $68,313 in traded volume before settling. So the prediction market has been right recently—but past performance is no guarantee of future results.

For now, traders are bracing for a potentially softer open, but with key data and Fed commentary on deck, the day could go either way.