Users of crypto-backed prediction market Polymarket were overwhelmingly taken off guard this morning by Kamala Harris’ choice of Minnesota Governor Tim Walz—a dark horse contender—as her running mate, upending millions of dollars worth of bets.

For the last week, Pennsylvania Governor Josh Shapiro was the market’s runaway favorite, commanding odds above 60% until just minutes before Harris instead chose Walz to be her choice for vice president.

Just four days ago, Walz, an outspoken Midwestern progressive with almost no national profile, hovered at a meager 4% odds of getting tapped by Harris to join the Democratic ticket.

Walz’s Polymarkets odds climbed yesterday—but only to about 30%—when it was widely reported that Harris had whittled down a shortlist of potential running mates to either him or Shapiro.

Then, early this morning, the Democratic VP calculus shifted on its head. The comments section on Polymarket’s VP bet went haywire after a tweet from a Minneapolis-based reporter revealed “a flurry of activity” and a fleet of vehicles arriving at Walz’s home.

Within a span of fifteen minutes, Walz’s Polymarket odds skyrocketed from 37% to 73%. Betting activity on the site became so frantic that Shapiro’s odds, while nonetheless plummeting, remained above 30% at the same time. Reloading the Polymarket site would generate new odds for Shapiro and Walz with almost every page refresh, a Decrypt reporter observed.

While Polymarket got Harris’ VP pick wrong in the macro sense, odds on the site flipped to Walz 18 minutes before CNN became the first major news outlet to officially report that the Minnesota politician, a former teacher, had been selected.

All in all, bettors had $125 million riding on who Harris would select to join her in taking on former president Donald Trump and Sen. J.D. Vance (R-OH) in November.

Today’s news is certainly cause to celebrate for a select subset; a $100 bet on Walz made on Friday would have netted more than $2,000 today.

Edited by Stacy Elliott.