Stanford Research Flags Manipulation Risk in Polymarket’s Short-Term Bitcoin Contracts

A new academic study has found that Polymarket’s five-minute Bitcoin prediction markets create conditions that allow traders to manipulate settlement prices, shifting money away from retail participants.

How the Manipulation Works

Researchers from Stanford University and Singapore Management University examined contracts where users bet on whether Bitcoin’s price would finish above or below a set level after five minutes. Since these contracts settle based on Chainlink price feeds capturing Bitcoin’s price at the exact end of each window, the setup gives traders a reason to push the spot market in their favor right before that moment.

What the Data Showed

Looking at trading patterns since Polymarket launched these contracts in July 2024, the team spotted noticeable spikes in Bitcoin spot-market orders just before settlement, followed by quick price snapbacks. This pattern lines up with deliberate settlement manipulation. By their estimate, roughly $1.28 million shifted from regular traders to manipulators over the study period.

A Possible Fix

Extending the contract window from five minutes to 15 minutes largely removed the problem, the researchers found. They noted this doesn’t mean prediction markets are broken by design, but rather that settlement mechanics matter. Options like longer windows or time-weighted average pricing could help, they said.

Wider Implications for Financial Markets

The paper adds that traditional exchanges like Nasdaq and Cboe are exploring similar event contracts, making settlement design a bigger issue as prediction markets move further into mainstream finance.

Prediction Markets See Record Activity

The findings come as the sector booms. Kalshi processed about $9.4 billion in June trading volume, largely driven by World Cup betting, while Polymarket handled roughly $4.3 billion. Combined World Cup winner markets alone have generated over $5.4 billion.

Growth has brought legal pressure too. Multiple US states have challenged Kalshi and Polymarket this year, while the CFTC maintains it holds exclusive authority over these contracts. The dispute is now working through federal courts and could eventually reach the Supreme Court.