More than $350 million in bets have been placed on the outcome of New York City’s mayoral race — and it will be a landslide election, if the betting markets are to be believed.

The Democratic nominee, Zohran Mamdani, has a 91 percent chance of winning the election on November 4, according to the largest online prediction market, Polymarket. Mr. Mamdani’s main challenger, Governor Andrew Cuomo, a Democrat-turned-independent candidate, has only a 9 percent chance at winning, according to the betting site. The Republican candidate, Curtis Sliwa, has less than 1 percent chance.

The overwhelming odds for Mr. Mamdani to win reached an apex on Monday, when his chances at winning hit 95 percent on Polymarket. The 34-year-old state assemblyman and self-declared socialist is also leading in all major polls by double digits.

Early voting started in New York on Saturday. The Cuomo campaign is trying to spin a surge in early voters — more than five times as many New Yorkers voted in the first day of early voting as did on the first day four years ago — as a sign that Mr. Cuomo is on his way to an upset victory.

The Cuomo campaign points to a Gothamist article that cites data showing more than 50 percent of early voters were over the age of 55 — a demographic that favors Mr. Cuomo. A new Suffolk poll released Wednesday also shows Mr. Cuomo gaining ground against Mr. Mamdani, but he is still 10 points behind.

Polymarket isn’t the only betting platform seeing a surge in mayoral election wagers. On another popular prediction market, Kalshi, more than $45 million in trades have been made so far on the outcome of the mayoral election. On this platform, Mr. Mamdani has a 92 percent chance at victory. The odds of Mr. Cuomo winning are rated at 8 percent, with Mr. Sliwa having a 2 percent shot.

The Cuomo campaign is downplaying the betting markets. The day before June’s Democratic mayoral primary, Polymarket had Mr. Cuomo with a 66 percent chance at winning the mayor’s race. Mr. Mamdani beat Mr. Cuomo in the primary by 12 percentage points.

“We were at about that at one point in the primary,” Mr. Cuomo’s spokesman, Rich Azzopardi, tells The New York Sun by email. “It’s all vapor. The only market that counts is the one with a ballot scanner attaches to it and so far so good.”

More than $306 million worth of trades have been made on Polymarket alone for this mayoral race, where betters can also wager on by what percentage Mr. Mamdani or another candidate will win. Odds on Polymarket are not determined by so-called experts looking at polling data but rather by the bettors themselves. Odds change in real time and are based on how much traders are willing to buy or sell shares of a predicted outcome. Money talks, not polls.

Political strategists have mixed opinions about whether the betting markets should be taken seriously as gauges of electoral outcomes. More than $3.2 billion in trades were made on the cryptocurrency-based Polymarket on the 2024 United States presidential election. While polls showed the race as essentially a coin toss up until Election Day, Polymarket had President Trump with a 58 percent chance of winning and Vice President Kamala Harris at 42 percent. The betting markets beat political pollsters.

One theory of why betting markets may be a more accurate predictor of outcomes is that when money is at stake, people are less likely to virtue signal by giving a response they think the pollster wants to hear. In 2016, polls failed to capture Mr. Trump’s lead because of the so-called secret Trump voter. 

“BREAKING: Zohran Mamdani soars to new record highs in the NYC Mayoral Election. 95% chance he’s New York City’s next mayor,” Polymarket’s X account posted on Monday.  

A user replied with a screenshot of the New York Times estimating Secretary Hillary Clinton had a 91 percent chance of winning the 2016 presidential election. “We’re not the NYTimes,” Polymarket replied.

Mr. Sliwa is also downplaying the betting markets. “I am not a gambler. I only gamble with my life. I have no response to the betting market,” he told the Sun via text message.