Buterin Urges ‘Median-of-3’ After Paris Weather Tampering

On April 6 and April 15, temperature readings from a Météo France sensor at Paris-Charles de Gaulle Airport briefly exceeded Polymarket’s 21°C settlement threshold, producing roughly $34,000 in payouts on the prediction platform.

Investigators say a person directed a hand dryer at the airport sensor, temporarily raising the recorded temperature. Météo France reported the incident to the Roissy air transport gendarmerie brigade for “alteration of the operation of an automated data processing system.” The altered readings were the basis for settlement in Polymarket’s Paris weather market.

Ethereum co-founder Vitalik Buterin wrote on social media that markets should use multiple independent data feeds. He posted: “Between this and the Myrnohrad incident, it’s pretty clear that a median-of-3 independent sources (if not more) for anything like this should be basically mandatory.” He referenced a November 2025 case in Myrnohrad, Ukraine, where a market settled on corrupted or erroneous data produced a roughly 33,000% payout.

Polymarket has faced ongoing scrutiny over the potential for manipulation when markets rely on a single data source. The platform has disclosed steps intended to address insider trading and other integrity concerns. Polymarket provided no comment on pending investigations into the Paris sensor readings.

Buterin also recommended expanding conditional markets, which settle outcomes based on the result of a related earlier event. He has described conditional markets as a way to tie settlement to linked, verifiable events rather than a single measurement. He has previously reported making a $70,000 wager against so-called “crazy mode” positions on Polymarket when he judged odds to be unreasonable.

The Paris sensor incident and the November 2025 Myrnohrad case have prompted discussion among market operators, data providers and technologists about settlement design. Participants are considering measures such as using multiple independent feeds, cross-checking sensors and adding rules that require corroborating evidence before finalizing high-value payouts.