Key Takeaways:
Researchers at Stanford University identified evidence that traders manipulated Polymarket's 5-minute Bitcoin prediction markets, extracting $8.2 million from retail bettors.
"The pattern is consistent with settlement manipulation — a structural vulnerability in contracts that settle on a price traders can move by trading the underlying asset itself," Shihao Yu, assistant professor at Singapore Management University and co-author of the paper, wrote in a LinkedIn post.
The paper, "Settlement Manipulation in Prediction Markets" by David Dai, Ruizhe Jia and Shihao Yu, examined Polymarket's binary contract launched Feb. 12, 2026, which paid $1 if Bitcoin closed a 5-minute window above its open and $0 otherwise. Within months, the 5- and 15-minute crypto up/down markets traded more than $4 billion, tripling the platform's daily volume. The contract settled against a Chainlink oracle averaging Bitcoin's price across major spot exchanges. The researchers found that Binance, the largest crypto exchange, sat about 2.5 basis points from the oracle and moved near one-for-one with it, finishing on the same side of the strike as the resolution about 85% of the time. Net order flow in the final 10 seconds before each close jumped about 50% above the pre-launch level, with the spike concentrated in the 6% of cycles the market judged near-even. Within 10 seconds of settlement, the price reverted by about a quarter in those cycles — a pattern consistent with manipulation rather than genuine information flow.
Just 821 traders — about one in 300 of the 243,000 who traded the contract — fit the manipulator profile, taking $8.2 million in pushed cycles while breaking even in the rest. Of the losses, 93% fell on retail. The researchers found no evidence of manipulation in the 15-minute contract, where a longer window diluted the impact of last-second pushes. Polymarket said it plans to transition certain markets to settlement methods using prices over a longer period rather than a single point in time, a change the company said would "further ensure market integrity."
The findings come as regulators intensify scrutiny of prediction markets. The Czech Finance Ministry added Polymarket to its blacklist of unauthorized online gambling websites on Monday, requiring internet service providers to block access within 15 days under the country's Gambling Act. The European Securities and Markets Authority warned on July 3 that many prediction market contracts could already fall under existing restrictions on binary options if they meet the definition of financial instruments, adding that firms cannot avoid EU rules by marketing binary-style products as "event contracts."
The research also carries implications beyond crypto. Cboe Global Markets has begun rolling out prediction products tied to stock indexes, while Nasdaq has sought approval for similar contracts. The paper's authors argue that any binary contract settling against a single price point — whether on Bitcoin, equity indices or commodities — carries the same structural vulnerability.
Polymarket said it uses multiple independent pricing oracles to aggregate data and ensure accuracy. The company is looking to transition certain markets in the next year to settlement methods that use prices over a longer period rather than a single point in time, which would "further ensure market integrity," a spokesperson said.
This article is for informational purposes only and does not constitute investment advice.
