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Banking & Compliance

Half The Volume Came From Trades Of Exactly $5,500: Kalshi And Polymarket Face Wash-Trading Questions, A CFTC Probe And $40bn Valuation Talks In The Same Week

Prediction markets went from curiosity to $45bn-a-month asset class in a year, and this week the scrutiny caught up. A CNBC analysis found that on 20 September nearly half the dollar volume in Kalshi's ether perpetual futures came from trades sized between $5,495 and $5,505, with 24-hour volume far out of line with resting liquidity; the CFTC is examining those trades, and Kalshi ended a trader incentive programme. On Polymarket's international exchange, observers flagged markets where the least likely outcomes attract more activity than the favourites. Both companies deny wash trading. At the same time Kalshi is reportedly discussing a raise at a $40bn valuation and Polymarket above $20bn, Kalshi holds about 80% of US market share, and the Fed's October decision is now priced on these venues - an 84% chance of a hold after the jobs report - and quoted by the financial press as fact. For compliance teams, brokers and anyone using these probabilities as signals, here is what the numbers mean.

AlchmAI Editorial11 min read

~50%

Of dollar volume in Kalshi's ether perpetuals on 20 September that came from trades sized $5,495-$5,505, per CNBC's analysis

$45bn

Combined monthly volume across Kalshi and Polymarket in August, up from under $5bn a year earlier; about 80% of Kalshi's is sport

$40bn

Valuation at which Kalshi is reportedly discussing a raise; Polymarket is raising above $20bn

84%

Probability of a Fed hold in October priced on these venues after the jobs report - and quoted as the market's view

A market that grows ten-fold in a year attracts two things: capital and scrutiny. Both arrived this week. CNBC's investigation of Kalshi's perpetual futures on ether found that on 20 September nearly half of the dollar volume came from trades sized between $5,495 and $5,505 - a clustering that a user had flagged as odd - with 24-hour volume abnormally high relative to the liquidity actually resting in the book. The Commodity Futures Trading Commission is examining the trades, and Kalshi has since terminated a trader incentive programme. On Polymarket's international exchange, which sits outside US oversight, observers highlighted a recurring quirk: in multi-outcome markets on elections, sport and central-bank decisions, the least likely contracts often see more activity than the favourites. Both companies deny that wash trading is taking place.

The commercial context makes the questions sharper. Combined monthly volume on the two platforms rose from under $5bn in September 2025 to more than $50bn by July and $45bn in August; Kalshi holds roughly 80% of US share and has reported more than $1bn of annualised revenue. Kalshi is reportedly in talks to raise at a $40bn valuation, Polymarket above $20bn. Nasdaq, Cboe, DraftKings, Coinbase and Robinhood have entered or signalled interest; Cboe announced KPI-linked binaries on its regulated exchange this week. And the venues' probabilities have become part of the financial conversation: when the September jobs report landed, the headline that the Fed was 84% likely to hold came from these markets.

What Surveillance Would Look For

  1. 01Size clustering. A large share of volume at one precise ticket size, as in the ether case, is the classic signature of automated or incentivised activity rather than organic demand.
  2. 02Volume versus depth. Reported turnover far above resting liquidity means trades are matching without the book absorbing risk - consistent with participants trading with themselves or with a counterparty they control.
  3. 03Longshot concentration. Unusual activity in low-probability contracts can reflect incentive mechanics, fee structures or attempts to move headline probabilities cheaply.
  4. 04Incentive-programme correlation. Volume that tracks the start and end of rebate or reward schemes rather than news is a flag; Kalshi's termination of its programme will provide a natural experiment.
  5. 05Cross-venue consistency. The same question priced very differently on two venues, or a probability that moves without corresponding news, is the kind of anomaly a surveillance system should raise automatically.

What It Means For Different Readers

  • Compliance teams at brokers offering event contracts: the obligations that apply to any venue - best execution, suitability, surveillance - apply here, and the regulator has just shown it is looking. Treat prediction-market products with the same market-abuse monitoring as derivatives.
  • Anyone using prediction-market probabilities as signals: weight them by liquidity and recent volume quality, not by headline turnover. An 84% Fed-hold probability on a deep, news-driven market is informative; a 70% on a thin market with clustered tickets is not.
  • Platforms building agents that act on these probabilities: debounce, require the level to hold with real volume behind it, and record the source and time with every order - the controls we described for Public's new agents apply doubly.
  • Investors in the venues: $40bn and $20bn valuations are bets on volume being real and regulation being manageable. This week put both assumptions in play.

The UK Dimension

The FCA is reviewing its 2019 position on binary options as prediction markets grow, and this week's events are the strongest argument for doing so carefully rather than quickly. A UK framework that treats event contracts as regulated derivatives with full surveillance, rather than as gambling or as unregulated novelties, would let London offer what the US venues are now scrambling to prove: probabilities you can trust because someone is watching the order book.

“A prediction market sells a number. The only thing that makes the number worth buying is that the volume behind it is real. This week, for the first time, that is being checked.”

The Bottom Line

Prediction markets reached $45bn a month, $40bn and $20bn-plus valuation talks, 80% US share for Kalshi and the status of the market's own forecast of the Fed - and this week CNBC found nearly half of one Kalshi market's volume in trades of almost exactly $5,500, the CFTC began examining it, Kalshi ended an incentive programme, and Polymarket's longshot activity drew questions, with both venues denying wash trading. The lesson is that in a market whose product is a probability, volume quality is everything, and surveillance for size clustering, volume-versus-depth, longshot concentration and incentive correlation is what makes the probability worth using. That applies to brokers offering the contracts, to anyone trading on the numbers, and to the agents now acting on them. Compliance and surveillance systems for new instruments are what we build as a fintech AI agency in London, and this week showed exactly which anomalies they need to catch.

References & Further Reading

Compliance & Regulatory Systemsprediction marketsmarket surveillanceKalshiPolymarketAI Signal & Stock Rating IntegrationFintech AI Agency London
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AlchmAI Editorial

Research and analysis, London

The AlchmAI team writes about the markets, technology and regulation we work with every day. We build trading platforms, real-time charts and AI analysis tools for brokers, prop firms and fintech teams from our office in Mayfair, London. Every article lists its sources. Nothing we publish is investment advice.

This article is general information and commentary. It is not investment advice or a recommendation to buy or sell any investment. Important information

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