As online prediction markets skyrocket in popularity, two major players have emerged as industry leaders: Kalshi and Polymarket.
Kalshi has mostly done things by the books, cozying up to the federal government in search of regulation and unmitigated approval. Meanwhile, Polymarket has seemed to make its own rules, letting users bet on controversial topics like civil war and nuclear detonation to rake in massive profits.
Both are vying for the cultural and financial status of being the one prediction market to rule them all—and reports suggest that behind closed doors, the men running the companies are taking it personally.
Here’s what to know about the two platforms, their CEOs, and the apparent growing beef between them.
Who are the Kalshi and Polymarket CEOs?
Kalshi is run by Tarek Mansour, a former Wall Street trader with a degree from MIT. Polymarket’s CEO is Shayne Coplan, an NYU dropout who grew up trading cryptocurrencies online.
The pair’s diverging backgrounds appear to have shaped their approaches to the burgeoning prediction market industry: Mansour has seemed to prioritize federal approvals and caution in Kalshi’s growth, while some critics say Coplan has speedrun his company’s scaling and overseas presence, regulations be damned.
How have Kalshi and Polymarket differed in their business?
Those differences are also reflected in the events that each prediction market hosts. While both Kalshi and Polymarket let users bet on topics like election outcomes, awards show results, and economic trends, only Polymarket has veered into the truly controversial.
Earlier this month, it came under fire for an event titled “Nuclear weapon detonation by…?” where users could bet on how soon a nuclear bomb would detonate, garnering immense backlash online over fears that insider trading could lead directly to a third World War. Polymarket then deleted the event.
How has the rivalry affected them?
Mansour and Copeland’s feud is playing out in business decisions, like their competing trademark applications for “the world’s largest prediction market” as reported by NPR, and in pettier shots, like Mansour’s admission that his team asked influencers to post memes dissing Polymarket after Coplan’s home was raided by the FBI in 2024. “Some of our team got pretty heated,” he said on a since-deleted podcast segment at the time.
But Mansour also believes his competition with Coplan is for the best. In a December interview, he compared it to the mid-2000s rivalry between NFL quarterbacks Tom Brady and Eli Manning: “When Tom Brady kind of reflected on that back in the day, he’s like, ‘You know, we were like the most ferocious on the field, and we fought each other,’” Mansour said, reasoning that his feud with Coplan is similary pushing them both to do their best work.
Kalshi and Polymarket did not respond to Fast Company’s request for comment.
Not the only rivalry in big tech
Mansour and Coplan’s rivalry calls to mind another feuding tech duo: OpenAI’s Sam Altman and Anthropic’s Dario Amodei. Their arc is more allies-to-enemies, with Amodei founding Anthropic in 2021 after leaving OpenAI over creative and strategic differences from Altman.
In the years since, the two have awkwardly rubbed elbows at industry events—literally. At the India AI Impact Summit this February, 13 leaders in tech joined hands and lifted their arms as if taking a bow. Altman and Amodei, who wound up next to each in line, were the only two not to join hands, instead letting their raised arms hover near each other.
What’s the latest in the OpenAI and Anthropic rivalry?
The companies were again put in sharp contrast at the end of that month, when Anthropic lost its deal with the Pentagon after refusing to give the Department of Defense permission to use its tech for fully autonomous weapons and mass domestic surveillance. In response, President Donald Trump blacklisted Anthropic’s tech from use by any government agency, and Defense Secretary Pete Hegseth designated Anthropic as a supply chain risk.
The same day Anthropic’s deal fell through, OpenAI signed its own deal with the Pentagon—presumably, one without the safeguards that stopped Anthropic’s deal from coming to fruition—leading many AI users to protest its products and instead use Anthropic tools like Claude, which jumped over OpenAI’s ChatGPT to become the No. 1 free app in the United States.
After OpenAI’s deal, Amodei shared a company memo internally at Anthropic (as reported by The Information) explaining that the government’s dislike for the company was because “we haven’t given dictator-style praise to Trump (while Sam [Altman] has).”
“I want to be very clear on the messaging that is coming from OpenAI, and the mendacious nature of it,” Amodei wrote. “This is an example of who they really are.”
The bottom line?
The public backlash to OpenAI’s Pentagon deal matches the response to Polymarket’s nuclear detonation event. Both companies crossed an ethical line for consumers that their competitors avoided, suggesting that a little healthy competition not only encourages tech companies to improve their product, but could push them to do so with morality in mind. And the social media response has suggested that when businesses are neck and neck in terms of quality, consumers might just opt for the brand with a backbone.