Early one morning in November 2024, Shayne Coplan, the founder of Polymarket, awoke to an unexpected visit. A group of F.B.I. agents burst into his New York apartment with a battering ram, scouring for evidence of illegal betting on his platform.
On social media, Mr. Coplan dismissed the raid as a politically motivated attack by the Biden administration. But privately, he and his advisers voiced suspicions about a different culprit, whom they blame for many of Polymarket’s problems: Tarek Mansour, the chief executive of Kalshi, Mr. Coplan’s biggest rival in the booming business of prediction markets.
Mr. Mansour’s company had indeed played a role. In the months before the F.B.I. raid, Kalshi’s lawyers met with federal prosecutors in Manhattan to raise concerns about Polymarket, according to four people with knowledge of the discussions, which have not been previously reported. The lawyers explained how Polymarket’s platform worked, one of the people said, and highlighted an important fact — that customers could use it from the United States, where it was supposed to be banned.
It was a moment of maximal aggression in a long-simmering feud between Kalshi and Polymarket, two of the tech industry’s hottest start-ups. A clash of ambitious founders is nothing new in Silicon Valley, where ego-driven squabbles are as familiar as corporate puffer vests. Uber and Lyft battled to rule the ride-hailing industry, and the billionaire-on-billionaire mudslinging between Sam Altman of OpenAI and Dario Amodei of Anthropic has become an intriguing subplot in the artificial intelligence world.
But the competition between the 28-year-old Mr. Coplan and the 30-year-old Mr. Mansour goes far beyond the normal bounds of corporate rivalry. Both are newly minted billionaires, intent on dominating prediction markets, which offer betting odds on sports, politics, culture and nearly everything else. By most accounts, they also despise each other with a fervor that has seeped into how their companies interact at virtually every level, according to interviews with more than 40 people in their circles, who spoke on the condition of anonymity to discuss sensitive dynamics.
“It’s just bad blood,” said Dustin Gouker, who writes a newsletter about prediction markets. “It’s become personal.”
The competition has raged in corporate meetings and the halls of Congress, shaped the regulatory debate in Washington and drawn unusual levels of attention and concern. Kalshi and Polymarket have filed competing trademark applications, jockeyed for the same deals, courted the same talent, sniped at each other in the press and engaged in name-calling on social media. They have each forged a business relationship with Donald Trump Jr., a common strategy in President Trump’s transactional Washington.
Both companies have “crossed the line in some ways,” said Noah Zingler-Sternig, a former Kalshi employee who runs a prediction market investment fund. “It can make public perception of the two companies less serious.”
The mutual loathing is not just about market share. It is a deeper rift over character and business ethics. Kalshi presents itself as a responsible actor that waited to secure regulatory permission to operate in the United States; Polymarket forged ahead without a license and still runs its main platform offshore. Kalshi has “know your customer” rules and bans certain sensitive topics; Polymarket lets customers sign up without sharing personal information and bet on things like the timing of Israeli missile strikes.
Mr. Coplan and Mr. Mansour have met over the years but rarely see each other these days, preferring to bad-mouth from afar. A self-described “math nerd” who graduated from M.I.T., Mr. Mansour has compared the prediction market rivalry to the healthy competition between the former pro quarterbacks Tom Brady and Eli Manning. Lately, however, he has also called Polymarket’s actions “illegal” and “immoral,” and pointed out that its overseas site is operated by a business entity in Panama.
“I don’t know what the laws of Panama are on insider trading on prediction markets,” Mr. Mansour said at a conference in Washington in April. “Probably nonexistent.”
Mr. Coplan, a skilled pitchman who dropped out of New York University, seldom mentions Kalshi in public. But he has called the company a “Polymarket copycat” and believes that Mr. Mansour has set out to sabotage him, two people with knowledge of his thinking said. He is convinced that his site is the best prediction market.
“It’s the most accurate thing we have as mankind right now,” Mr. Coplan said on “60 Minutes” last year.
Elisabeth Diana, a Kalshi spokeswoman, said the company had learned about the F.B.I. raid from media reports. Kalshi routinely discusses compliance issues with the government, she added, and has been vocal in pointing out “public issues with a company that is endangering consumers and sullying the industry.”
Mr. Mansour has “no personal animosity towards Shayne,” Ms. Diana said. “The only issue Tarek has with Shayne is his reckless approach to an industry that Kalshi has spent years getting regulated.”
A Polymarket spokeswoman shared a one-line statement about Mr. Mansour, a quotation by Ralph Waldo Emerson: “The louder he talked of his honor, the faster we counted our spoons.” She said Polymarket has protocols in place to stop insider trading, resulting in nearly 100 referrals to law enforcement. “We are committed to maintaining accurate, fair and transparent markets,” she said.
As prediction markets transform from a niche pursuit into a cultural phenomenon, both companies face mounting regulatory threats. Kalshi and Polymarket are battling in court with a procession of state attorneys general who say the companies’ sports offerings violate gambling laws. Polymarket is also being investigated by the Commodity Futures Trading Commission, the U.S. regulator that oversees prediction markets.
Kalshi’s warnings about Polymarket have become much more overt. In May, Brian Quintenz, a former C.F.T.C. commissioner who serves on Kalshi’s board, shared a message on X describing Polymarket’s protocols for screening users.
He tagged an account belonging to a potentially interested party: the U.S. attorney’s office for the Southern District of New York.
Two Rivals Collide
A lifelong New Yorker, Mr. Coplan founded Polymarket in 2020, working out of an apartment in Lower Manhattan, where he set up a laptop in a makeshift “bathroom office.” He viewed himself as an upstart, pioneering a technology far outside the mainstream.
He had a formidable rival. A former Citadel trader who had grown up in Lebanon, Mr. Mansour started Kalshi in 2018 with Luana Lopes Lara, an M.I.T. classmate who serves as the firm’s chief operating officer. Mr. Mansour’s colleagues describe him as smart, scrappy and a bit awkward; Mr. Coplan is more easygoing, an art collector and music aficionado who cultivates a studied New York cool.
They have never been particularly friendly. In one stilted early encounter, Mr. Coplan pointed out to Mr. Mansour that both were raised by single mothers, a comment that made Mr. Mansour uncomfortable, a person familiar with the exchange said.
But the two men share a conviction that prediction markets will transform finance and media, harnessing the “wisdom of the crowd” to provide a valuable new source of information. Bets on Polymarket and Kalshi are structured as yes-or-no questions, with topics that range from the weather to the Super Bowl; the amount that users collectively wager determines the odds of a particular outcome.
Before it started offering these bets in 2021, Kalshi sought a license from the C.F.T.C. to run a prediction market. During early discussions with the agency, Kalshi was already raising concerns about Polymarket, three people familiar with the matter said.
The primary messenger was Jeff Bandman, a Kalshi strategist, who urged the C.F.T.C. to look into Mr. Coplan’s firm, pointing out that it was available in the United States without proper authorization, one of the people said. In January 2022, the agency fined Polymarket $1.4 million for operating an unregistered platform; Polymarket agreed to stop accepting bets from customers in the United States.
The ban opened the door for Kalshi to dominate the U.S. market. But first the company would have to fight the government for friendlier rules. Under President Joseph R. Biden Jr., the C.F.T.C. prohibited bets on elections. Kalshi sued the agency in 2023.
While the legal battle tied up Kalshi, Polymarket turned into a mainstream sensation, despite its U.S. ban. With a few clicks, Americans could gain access to the website through virtual private networks, an online tool that disguises a user’s location. Polymarket’s odds became a major talking point before the 2024 presidential election, when the site showed that Mr. Trump had a clearer advantage than polls suggested.
“They didn’t do the regulatory,” Mr. Mansour said on a podcast in June. “They just launched. They didn’t care.”
Shortly before the election, Kalshi defeated the C.F.T.C. in court, paving the way for licensed prediction markets to operate in the United States. Polymarket still lacked that seal of regulatory approval, even as the platform’s surging popularity turned Mr. Coplan into an overnight celebrity.
In 2024, prosecutors in the Southern District of New York pursued an investigation into whether Polymarket was violating the prohibition on U.S. users. The week after Mr. Trump’s election victory, the F.B.I. conducted the raid of Mr. Coplan’s Manhattan apartment and seized his electronic devices.
Kalshi pounced. Keaton Inglis, a Kalshi employee, reached out to the former National Football League star Antonio Brown, directing him to post a message on X calling Mr. Coplan “guilty,” according to screenshots published in Pirate Wires, a tech publication.
Mr. Brown later apologized, saying he had been “doing other business with Kalshi and just tweeted it.” Mr. Mansour also expressed regret. “Some of our team got pretty heated,” he said on a December 2024 podcast.
The raid left Mr. Coplan and his allies deeply suspicious. Rumors about the incident circulated in the media with striking speed. Behind the scenes, Mr. Coplan and other Polymarket insiders speculated that a private investigator, hired by Kalshi or one of its allies, had tailed him, seen the F.B.I. arrive and shared the information with the press, four people familiar with the discussions said.
“This is a complete lie,” Ms. Diana of Kalshi said. “A truly bizarre level of paranoia.”
Trying to Sour a Deal
Last July, Mr. Coplan arrived for a business meeting at Manhatta, a downtown restaurant known for its sweeping 60th-floor views. He had dressed casually, and brought along a bagel in a paper bag.
Mr. Coplan’s dinner date was the billionaire Jeffrey Sprecher, who founded Intercontinental Exchange, the $80 billion giant that owns the New York Stock Exchange. It was a meeting of old and new — and a crucial moment in Polymarket’s rivalry with Kalshi.
Over the years, Kalshi had built a roster of blue-chip investors, including Sequoia Capital, a leading venture capital firm. Mr. Coplan had not always had the same success navigating large institutions. But he and Mr. Mansour both forged relationships with executives at Intercontinental Exchange, which wanted to invest in prediction markets.
Mr. Coplan and Mr. Sprecher hit it off at Manhatta. After considering a possible deal with Kalshi, Intercontinental Exchange instead struck an agreement to invest in Polymarket last fall.
Mr. Mansour was upset when he heard the news, a person familiar with his thinking said. Before the deal was announced, he and one of Kalshi’s investors, Alex Immerman of Andreessen Horowitz, each spoke with Intercontinental Exchange’s executive team, five people with knowledge of the conversations said.
Those people offered conflicting accounts of the talks. But the feedback from Mr. Mansour and Mr. Immerman came across as a last-ditch effort to dissuade Intercontinental Exchange from going through with the deal, three of the people said.
Ms. Diana said Kalshi was “not interested in the deal” with Mr. Sprecher.
In the end, Mr. Sprecher stuck with Mr. Coplan, unveiling a deal to invest up to $2 billion in Polymarket in October. It was part of a string of victories for Polymarket. Last July, the Southern District of New York dropped its investigation into Mr. Coplan, as the Trump administration pulled back on enforcement. That summer, Mr. Coplan also announced an investment from 1789 Capital, the venture firm part-owned by Donald Trump Jr.
“This admin is very pro-innovation, and pro-crypto, and pro-Polymarket, which is amazing,” Mr. Coplan said on “60 Minutes” last fall.
To capitalize on the friendly environment, Polymarket would need a license to operate in the United States. Mr. Coplan planned to buy a company that already had the necessary approval.
He faced a familiar obstacle: Kalshi. Mr. Mansour raised concerns with top C.F.T.C. officials about a pending application from Railbird, a little-known prediction market operator that was rumored to be Mr. Coplan’s acquisition target, five people familiar with the matter said.
Kalshi’s warnings went unheeded. The C.F.T.C. approved Railbird’s application in June 2025, and Mr. Coplan went on to buy a different firm, QCX, for $112 million, after it received a U.S. license around the same time. Polymarket’s main platform was still banned, but the QCX purchase allowed Mr. Coplan to roll out a smaller U.S. app, giving his company access to more customers.
When he announced the QCX acquisition in July, Mr. Coplan posted an image of the American flag on social media.
“I’ve waited a long time to say this,” he wrote. “Polymarket is coming home.”
A Subtle Act of Trolling
As the New York Knicks embarked on an epic playoff run this spring, Mr. Mansour posted a photo of himself under the lights at Madison Square Garden. He sat courtside, with a toothy grin, wearing Knicks colors.
Officially, Kalshi was celebrating a new partnership with the Garden, which had christened its sixth-floor concourse the Kalshi Concourse. But close observers picked up on something else: a subtle act of trolling.
Mr. Coplan had posted frequently about the Knicks before he was famous, and had been spotted courtside at the Garden during the regular season. Before Kalshi secured the partnership with the Garden, Polymarket had explored a similar deal but was unwilling to match Kalshi’s offer, a person familiar with the discussions said.
It was a sign that a rivalry once confined to an internet niche had exploded into the mainstream. Over the first six months of the year, Kalshi and Polymarket have drawn more than $150 billion in trades, a 1,200 percent surge that has raised the competitive stakes.
So far, Mr. Mansour is winning.
After a fund-raising round in May, Kalshi was valued at $22 billion — $7 billion more than Polymarket. Last month, Kalshi processed over $33 billion in trades, twice Polymarket’s total, according to The Block, a data provider.
Ms. Diana said it was “laughable” to suggest that Kalshi’s deal with Madison Square Garden had something to do with Mr. Coplan. “We don’t do deals to troll people,” she said.
The skyrocketing interest in prediction markets has also brought heightened political scrutiny, much of it focused on Polymarket. In April, an Army Special Forces soldier was charged with using confidential information to place bets on Polymarket about the capture of Venezuela’s president, Nicolás Maduro. The soldier had made more than $400,000, using the company’s offshore platform through a VPN, according to the indictment. (Polymarket’s spokeswoman said the company bans VPNs.)
Kalshi and Polymarket are taking divergent approaches to policing insider trading. Kalshi requires customers to provide detailed personal information, sometimes including employment status, before they place a wager. Polymarket’s platform creates a public record of trades, allowing sleuths to ferret out possible wrongdoing. But it does not mandate that users reveal their name, employer or other personal information.
That model is common in the crypto world, where customers “like to kind of live under the table,” said Aj Pleasanton, an influencer who is a paid partner of Polymarket.
Behind the scenes, Mr. Mansour has grown increasingly furious about Polymarket’s business approach and sometimes calls Mr. Coplan’s chief legal officer, Neal Kumar, to express his outrage, two people familiar with the matter said.
The clashes happen so frequently, it can be difficult to keep track of them. In the spring of 2025, influencers on Polymarket’s payroll amplified news that a business partnership Kalshi announced with Elon Musk’s A.I. effort, xAI, had fallen through, according to a person familiar with the matter and documents reviewed by The New York Times.
Later that year, Polymarket hired Max Crowley, an early Uber employee, to serve as vice president of partnerships. After less than two months, Mr. Crowley quit and joined Kalshi, angering Mr. Coplan. Between jobs, he received legal threats from Mr. Coplan and Alex Spiro, a lawyer who has joined Polymarket’s board, though no lawsuit materialized, a person familiar with the matter said.
Polymarket and Kalshi do not collaborate even in areas where their interests clearly align. When Kalshi announced that it was forming an advocacy group to fight state-level regulations on prediction markets, it joined forces with several companies, but not Polymarket.
The next month, Kalshi suffered a setback in one of the state cases — and a new gambling opportunity popped up on Polymarket’s website. It invited customers to wager on how soon Kalshi would have to wind down its sports betting operation in Massachusetts.
Sharon LaFraniere and Nicole Hong contributed reporting. Sheelagh McNeill and Kirsten Noyes contributed research.
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