Stanford study: 5-minute Bitcoin markets allowed manipulation

Researchers at Stanford University and Singapore Management University analyzed Polymarket’s five-minute Bitcoin prediction contracts and found that traders could influence Bitcoin spot prices at settlement. The study examined contracts that paid out if Bitcoin finished above or below a preset level after five minutes.

Polymarket resolved the contracts using Chainlink price feeds that sample the spot price at the end of each five-minute window. The paper says that created an incentive to trade in the spot market immediately before settlement to affect the final price used to resolve contracts.

The authors compared trading activity before and after Polymarket introduced the five-minute contracts in July 2024. They identified sharp increases in spot-market order flow in the moments just before settlement and rapid price reversals after contracts closed, patterns consistent with settlement-price manipulation.

Using transaction data from the sample period, the researchers estimated manipulators captured about $1.28 million from other traders. When Polymarket extended contract durations from five minutes to 15 minutes, the abnormal pre-settlement order flow largely disappeared.

The paper states, “results do not indicate prediction markets are inherently vulnerable to manipulation,” and recommends design changes to reduce the ability and incentive to move spot prices around settlement. Suggested fixes include longer settlement windows and pricing methods such as time-weighted average prices.

The authors noted the findings could apply beyond crypto platforms. Traditional exchanges including Nasdaq and Cboe have proposed event contracts tied to asset prices, and the paper warns short-duration contracts that resolve against a single spot price can create similar incentives.

Prediction markets posted large volumes in June as the expanded 2026 FIFA World Cup increased activity. The paper cites platform data showing Kalshi processed roughly $9.4 billion in trading volume that month and Polymarket International about $4.3 billion. World Cup winner markets on the two platforms later generated more than $5.4 billion combined, with Polymarket processing about $4.25 billion and Kalshi about $1.2 billion.

The sector’s growth has coincided with legal challenges in the United States. Several states have sued companies including Kalshi and Polymarket this year, while the Commodity Futures Trading Commission has argued federally regulated event contracts fall under its exclusive jurisdiction. The disputes are moving through the federal courts, and legal observers have said conflicting appellate rulings might prompt the U.S. Supreme Court to decide whether states or the CFTC have primary authority over prediction markets.