Polymarket and Kalshi Settle BTC Contracts Differently — and It Matters for Trading Bots

Both Polymarket and Kalshi now settle short-duration Bitcoin binary contracts using a 60-second average price rather than a single last-print snapshot, but the two platforms use different indexes and sampling methods. Polymarket relies on a Chainlink-computed time-weighted average price (TWAP) that can be tracked live throughout the contract slot, while Kalshi uses a simple average of the CF Benchmarks real-time index over the final minute before expiry. The shift away from snapshot settlement on both platforms was driven by documented manipulation, where brief price pushes at contract close created unfair outcomes for retail participants. Because the settlement mechanics differ, a trading bot trained on Polymarket's TWAP signal cannot be directly applied to Kalshi without recalibration — the underlying price references are not equivalent. Developers building automated strategies must first identify the exact settlement number each venue uses before constructing signals, backtests, or execution logic.