Stew, a 35-year-old from Montana, has enjoyed dabbling in sports bets since he downloaded the Kalshi app about 18 months ago. But just a few weeks ago, after spotting reports of elevated pizza deliveries around the Pentagon during some late-night scrolling, he made a different kind of bet - wagering $10 (£7. So-called predictions markets - overseen by firms such as Kalshi - have exploded in popularity over the last year, hosting more than $44bn in trades. They are rapidly transforming the betting landscape in the US, where sports betting was largely illegal until 2018 and gambling on elections had been off-limits for years until 2024. Kalshi also ended up cancelling the Khamenei market, which had drawn $54m in trades, noting that US-regulated entities are barred from "having a market directly settling on someone's death". Though the Biden administration had taken a hard line on the sector, proposing to ban sports and politics-related event contracts, that regulatory drive stalled after a court defeat and the 2024 election of Donald Trump, who came to power promising a lighter hand.