The S&P 500 surged on Thursday as easing concerns over the U.S.-Iran war and a rebound in semiconductor stocks sparked a broad market rally. Polymarket traders are betting the benchmark index will extend those gains at Friday’s open.

The S&P 500 climbed 1.75% to close at 7,394.30 on Thursday, recovering much of the prior session’s losses after President Donald Trump signaled that a peace agreement with Iran could be signed soon. The June 12 Polymarket contract implied an 83% probability that the index will open higher on Friday.

Why That Number Matters

Investor sentiment improved sharply after Trump said a deal with Iran was nearing completion and confirmed that planned U.S. strikes had been called off.

The president told reporters Thursday that a signing was expected soon and that ...