Kalshi and Polymarket's Sports Boom Rattles Manifest Purists

The annual Manifest convention in Berkeley wrapped up in June, and Bloomberg's dispatch captured a mood that says something about where prediction markets are actually going. The forecasting purists who spent years arguing that markets could improve public reasoning got their wish. Kalshi and Polymarket are now big, mainstream, and working with a friendly administration and with news organizations like Fox and CNN. The purists, per the reporting, are not happy about it.

The specifics behind that discomfort are the interesting part. Sports reportedly account for roughly 80 percent of trading volume on Kalshi and 39 percent on Polymarket since July 2024, according to Bloomberg. That is a lot of the venue's liquidity going into games rather than into the kind of world-event questions the community used to hold up as the whole point. One trader at Manifest, as Bloomberg quotes them, asked plainly what the truth-seeking value of prediction markets has to do with sports at all.

The absence itself is a signal. Kalshi and Polymarket had sponsored Manifest in past years, and this year they were AWOL. Both companies declined to comment on the change. Meanwhile, Meta is reportedly building a play-money prediction app called Arena and has explored partnerships with both platforms, which would be a distribution channel that pushes the mainstream, casual-bettor use case even harder.

The honest caveat is that Bloomberg's piece is a scene story, not a study. It does not quantify whether policy or election markets have become less accurate as sports volume has grown, and it does not say what Kalshi or Polymarket think about the criticism, because both declined to comment. So the 'signal is degrading' framing is a worry the purists voiced at Manifest, not a measured finding.

Still, the tension worth watching is which venues serve which purpose. If Kalshi and Polymarket keep leaning into sports and consumer distribution, the openings for smaller markets and research-oriented venues, the ones Manifest's crowd runs, get larger, not smaller. That is where AI-alignment forecasters and policy shops looking for cleaner odds on world events will end up shopping.