The bitter feud between the bosses of Polymarket and Kalshi has been even more vicious and petty than previously known – from battling over the affections of Donald Trump Jr. to the spreading of unsubstantiated, sex-drenched gossip, The Post has learned.
Shayne Coplan, the 28-year-old, shaggy-haired CEO of prediction market giant Polymarket, is recognized as the world’s youngest self-made billionaire with a net worth of $1 billion. Still, sources say Coplan has been consumed by an epic grudge match with Tarek Mansour, the 30-year-old, bespectacled CEO of archrival Kalshi.
Mansour – whose app, like Polymarket’s, allows users to bet on sports, the weather, the Oscars and celebrity breakups – has a fortune currently pegged at $2.6 billion.
Coplan has chafed over the fact that Kalshi – which he has branded a “copycat Polymarket” – has become bigger than Polymarket, sources said. Kalshi also reportedly tipped off the feds ahead of a November 2024 FBI raid of Coplan’s apartment in search of evidence that Polymarket was facilitating illegal gambling.
Coplan – who was never arrested or charged following the seizure of his electronic devices – has referred to Kalshi as “ratty,” according to sources.
But it’s with Mansour that Coplan’s animus has become decidedly personal. According to one insider, Coplan’s preferred nickname for Mansour around Polymarket’s New York City offices is “Little Tarek” – a reference to Mansour’s height, the source added.
Coplan also has repeatedly circulated an unconfirmed rumor about Mansour and his No. 2 exec Luana Lopes Lara – namely, that the pair used to date and that the relationship allegedly ended with Lopes Lara cheating on Mansour.
Kalshi spokeswoman Elisabeth Diana said Lopes Lara has never cheated on anyone, adding “Shayne should really focus on growing his company instead of spreading lies. WTF.”
Kalshi’s co-founders – who together have been the public face of the company, frequently appearing side-by-side for interviews at events and on podcasts – have never publicly indicated that they were ever romantically linked.
Nevertheless, insiders told The Post that when they were both students at the Massachusetts Institute of Technology it was understood in some circles that they were dating.
According to insiders, Coplan – who declared in a “60 Minutes” interview last November that Polymarket is “the most accurate thing we have as mankind right now” – has taken the rumor to another level.
Specifically, sources said Coplan has gone on to claim at parties and in office meetings alike that the relationship ended when Lopes Lara – a Brazilian-born math prodigy who did a stint as a professional ballerina before becoming the world’s youngest female billionaire last year – “cucked” Mansour.
The alleged cuckolding led to the couple’s breakup, Coplan has claimed in conversations with work colleagues, according to multiple sources close to the company. Coplan also would chuckle as he told the rumor, calling Mansour a “loser” for continuing to run a company alongside a woman who had allegedly cheated on him romantically, according to sources.
“Shayne would say that just to cut [Mansour] down in front of people,” one of the sources said. “He told it to me several times in his office to the point of it getting repetitive – It’s like your dad or grandad who’d tell you the same story like 50 times.
“I’d have to be like, ‘Yeah, I’ve heard that one already.’”
A Polymarket spokesman denied that Coplan has spread sexual rumors about Kalshi’s co-founders. The spokesperson added that Kalshi has stoked tensions between the two companies for years which has ultimately led to allegations like this surfacing.
“They have spent so much time and resources pushing hit pieces on Shayne and Polymarket to the detriment of both companies and the industry at large. We have never pushed this type of sensitive personal information and we are deeply sorry that this is now being reported on,” the spokesman said.
“This is an unfortunate consequence of them paying so many opposition firms to dig for dirt on us – but you reap what you sow.”
Mansour and Lopes Lara met while studying computer science at MIT before graduating together in 2018. They founded Kalshi that year. In 2019 they were accepted into Y Combinator, just as Sam Altman was stepping down as president of the influential startup accelerator to focus full-time on OpenAI.
It couldn’t be determined how long or whether their relationship lasted after finishing college. In May of this year, Lopes Lara said in a post on X that she “Married the love of my life today.”
Alongside the sick jokes and the insults, sources said Coplan has also been susceptible to fits of anger at the office – particularly upon hearing news of Kalshi’s success. In one instance early last year, insiders said Coplan allegedly became wildly irate when news broke that Donald Trump Jr. had joined Kalshi as a strategic advisor.
“Coplan screamed so loud that nearly the entire floor was startled,” said an employee who was there at the time.
Trump Jr. ended up also joining Polymarket as an advisor later that year in August. The appointment coincided with a strategic investment in the company for an undisclosed amount by 1789 Capital, the investment firm where Trump Jr. is a partner.
Despite his fresh-faced, smooth-talking public persona, multiple sources claim Coplan – an NYU dropout who founded Polymarket out of a pokey apartment on Manhattan’s Lower East Side – isn’t a “chill” boss, but instead a manager bent on control.
According to a source with knowledge, Coplan for a time had set up his office inside Polymarket’s kitchen – with employees guessing that he was looking to grill them about what they were working on as they came to get coffee.
Insiders also claim Coplan has a habit of screaming and berating employees about perceived mistakes, new markets he thinks Polymarket should be offering but isn’t, and bad press.
The latter included an exclusive story in The Post last month that detailed concerns inside Polymarket that Kalshi might be spying on its operations – an article that Coplan felt “made them all look nuts,” according to a source.
To cool off and clear his head, Coplan takes walks outside Polymarket’s offices in New York’s trendy SoHo neighborhood. But on multiple occasions over the past two years, an already stressed-out Coplan spotted Mansour strolling down Broadway, where Kalshi’s offices are less than two blocks away from Polymarket’s.
Following the chance sightings of Mansour – the two never stopped to speak – Coplan returned to the office visibly irritated, according to sources.
“He came back and shouted down the hall for someone to get over to him immediately,” one source said, adding that at times, Coplan has pulled his own hair during fits of rage.
A Polymarket spokesman disputed the account, calling it a “twisted, misrepresented story from three years ago, just to stir things up.”
Mansour – who has cultivated a scrupulous, by-the-book persona as he touts Kalshi’s regulatory compliance – has also been known to get petty and underhanded when it comes to Polymarket.
In January, Mansour shared a New York Times article about prediction markets. The Times headline read: “Betting on Prediction Markets Is Their Job. They Make Millions.” But Mansour appeared to scrub the text that came after: “Welcome to the era of the Polymarket sharp.”
In November 2024, shortly after the FBI raid on Coplan’s SoHo loft, tech blog Pirate Wires posted screenshots that showed Kalshi employees asking former NFL wide receiver Antonio Brown to quote-tweet a post about Coplan with the comment, “this [n-word] seem[s] guilty.” Brown, at the time a paid influencer for Kalshi, posted the message shortly thereafter.
Tom Schmidt, a venture-capitalist at the firm Dragonfly which has invested in Polymarket, said in an interview with The Post in May that Coplan was furious about the text messages and told him at the time: “These guys are so f–ing shady and ratty,” referring to Kalshi.
Last month, The Post reported that Polymarket had launched a probe of what it believed to be product leaks to Kalshi. In addition to assembling a dossier of suspicious incidents that pointed to a possible mole, Polymarket had some of the windows of one of its Manhattan offices tinted over concerns that executives across the street at Paradigm, a venture firm that backs Kalshi, could be spying on its offices.
In comments to The Post, a Kalshi spokesperson denied conducting any corporate espionage, adding: “This is sad and borderline delusional. Polymarket is welcome to waste its time investigating. While they do that, we’ll keep building.”
Kalshi, according to third-party analytics providers, has increasingly pulled ahead of Polymarket in terms of trading volume – an increasing source of frustration for Coplan, whose firm became a household name after its betting platform correctly predicted the surprise 2024 election of Donald Trump.
As recently as last August, Polymarket had logged more trading volume on its platform than Kalshi – but that has recently flipped. Roughly $31.5 billion was traded on Kalshi in June while Polymarket hosted $10.6 billion in trades, according to Dune Analytics.
Polymarket has raised roughly $2 billion since it was founded in 2020 and earned a roughly $15 billion valuation in a financing earlier this year. Kalshi has raised some $2.6 billion and was valued at $22 billion in a May funding round. Kalshi has reportedly been in talks for additional financing that could value it at $40 billion.
