Stanford research delves into manipulation risks of Polymarket Bitcoin contracts

How fast clearing forecasting markets change trading behavior

A new study by scholars at Stanford University and Singapore Management University points out that Polymarket's five-minute Bitcoin forecasting contract creates incentives for some participants to manipulate spot prices before settlement-which leads to a shift of value from less experienced traders to those who are good at exploiting time differences. The study examined short-term contracts based on settlement of the Bitcoin price relative to a fixed threshold at the end of each five-minute trading window. Because settlement relies on the Chainlink price feedback mechanism linked to the spot price at the end of the window, the paper concludes that traders have the opportunity to influence the reference price before the contract expires.

Core Discovery

The paper linked Polymarket's five-minute Bitcoin contract to an abnormal peak in order flow in the spot market before settlement. The researchers observed rapid price reversals around the settlement reference point consistent with manipulation behavior. The study estimates that approximately $1.28 million was transferred from ordinary traders to manipulators during the sample period. Extending the contract period from five minutes to 15 minutes "basically eliminated" this effect, indicating that contract design is crucial. Settlement mechanisms-rather than forecasting the market itself-appear to be a key risk factor, and solutions include extending the settlement window and adopting alternative pricing methods.

Short settlement windows may reward "price chasing" behavior

Polymarket's five-minute Bitcoin prediction market allows traders to bet on whether Bitcoin will be above or below a predetermined level after five minutes. These contracts are settled using Chainlink price feedback that references the Bitcoin price at the end of each trading window. The paper argues that this settlement method may distort incentives: When the reference price is set at a particular moment, savvy traders may find it profitable to push the spot market higher in the minutes or even seconds before this timestamp. In other words, the trading behavior of forecast contracts may be coupled with spot market execution just before settlement.

Researchers 'findings in order flow and price behavior

To test this claim, the researchers analyzed trading activity before and after Polymarket introduced these contracts in July 2024. They focused on the changes in spot market dynamics before and after the launch of the contract. The research report stated that order flow in the Bitcoin spot market increased sharply shortly before settlement, followed by a rapid price reversal after the five-minute window closed. The author combines buy/sell pressure before settlement with a reversal pattern after settlement, interpreting it as consistent with settlement price manipulation rather than a normal price discovery process. Although order flow alone cannot directly prove manipulation, the paper's reasoning is based on point in time: when a contract is settled based on a price snapshot at the end of a short window, traders can profit by targeting that snapshot rather than predicting long-term trends.

How much value is transferred-and how to reduce risk

The paper estimates that during the sample period, this behavior transferred approximately $1.28 million from "ordinary traders" to "manipulators." The specific mechanism seems to be related to who can effectively influence market prices at settlement times, which exposes others to consequences that are not of their own making. Importantly, the authors also report that extending the contract term from five minutes to fifteen minutes largely eliminated this effect. This result points to practical mitigations: The shorter the time between trade and settlement-especially if settlement relies on prices at the end of a single window-the more likely it is that incentives will revolve around instantaneous spot market strategies.

The study emphasizes that its findings do not mean that prediction markets are inherently susceptible to manipulation. Instead, risk seems to stem from settlement design. The researchers highlighted potential solutions, such as longer settlement windows and alternative pricing methods-such as time-weighted average prices-that reduce the margin for "hitting" a single reference timestamp.

Why is this important beyond cryptocurrency regulation

The impact is not limited to decentralized or cryptocurrency native platforms. The paper pointed out that traditional exchanges, including the Nasdaq and the Chicago Options Exchange, have proposed event contracts linked to asset prices. As prediction markets expand into more regulated financial areas, contract design may become a core issue for regulators and market designers. From an investor or trader's perspective, the study shows that the safest products are not just those with better liquidity or higher reputation, but also those with settlement logic that limits the link between contract settlement and immediate underlying market price changes. Therefore, readers should pay attention to how platforms set reference prices-whether using window end-of-window snapshots, TWAP-style metrics, or other anti-manipulation mechanisms-especially for short-term contracts.

At the same time, legal review of the forecast market in the United States continues to intensify. Earlier this year, multiple states challenged platforms such as Kalshi and Polymarket. In addition, the Commodity Futures Trading Commission believes that federally regulated event contracts fall within its "exclusive jurisdiction" rather than state gambling laws. The dispute is currently being heard in federal court, and observers say conflicting appeal decisions may ultimately require the U.S. Supreme Court to decide whether states or the CFTC has primary jurisdiction.

World Cup craze drives forecast market trading volume

Although the new study focuses on settlement mechanisms, the broader industry continues to grow in activity. As the 2026 FIFA World Cup sparked interest from platforms, the forecast market set record trading volume in June. According to DefiLlama data cited in the article, Kalshi handled approximately $9.4 billion in transaction volume in June, while Polymarket International handled approximately $4.3 billion. Total trading volume in the World Cup championship market exceeds US$5.4 billion, with Polymarket accounting for approximately US$4.25 billion and Kalshi accounting for approximately US$1.2 billion, according to data reported by the platform at the time of writing. The surge highlights why contract design issues may remain prominent: As trading volumes rise and markets shift from niche speculation to mainstream attention, the incentive to exploit structural weaknesses for economic benefits also increases as participation increases.

Looking ahead, the key question for traders, builders and regulators is whether the platform can expand the forecasting market without generating exploitable settlement dynamics-especially for ultra-short-term contracts. Findings from Stanford University and Singapore Management University suggest that changing the length of the settlement window and using price averaging methods can significantly reduce the risk of manipulation, but market participants want to see the extent to which these design changes are widely adopted and how quickly they can translate into cleaner spot market behavior.