Polymarket–Kalshi Cross-Platform Arbitrage (BTC 15-Minute Markets)

How It Works Polymarket and Kalshi both list short-duration (15-minute window) binary markets on BTC price outcomes. Because the two platforms have separate liquidity pools, order books, and user bases, the implied probabilities for the same event frequently diverge. A bot monitors both order books simultaneously and, when the spread between the NO price on one platform and the YES price on the other exceeds transaction costs, places opposing legs to lock in a guaranteed return regardless of the outcome.

Entry / Exit Conditions Entry is triggered when the sum of the best YES price on Platform A and the best NO price on Platform B is less than 1.00 (i.e., combined cost < $1.00 per share pair), creating a locked profit on resolution. The bot must execute both legs near-simultaneously to avoid leg risk — one leg filling while the other moves. Exit is automatic at market resolution; there is no active exit required since the position is fully hedged.

Verified Results No on-chain verified P&L is presented in the repository descriptions. The repos (haoo99, Crayz916, samuel483, lufegaga, kmjjjj) are largely educational or early-stage, with star counts of 0–5, suggesting limited public validation. The thesis is structurally sound and well-known in prediction market circles.

Implementation Notes Multiple repositories implement this in Python and Rust. The Rust implementation (kmjjjj) monitors BTC and SOL markets. PMXT (pmxt-dev/pmxt, 1915 stars, 225 forks) provides a unified API layer across Polymarket and Kalshi, significantly simplifying the cross-platform feed aggregation required. Execution latency is critical given the 15-minute market window; both legs must settle before resolution.

Risks - **Leg risk**: one leg fills, the other misses, leaving a naked directional position. - **Liquidity asymmetry**: thin order books on either platform can cause slippage that eliminates the spread. - **Resolution discrepancy**: the two platforms may use different price oracles or timestamps, meaning the same event resolves differently on each. - **Regulatory/platform risk**: Kalshi and Polymarket have different withdrawal mechanics, creating capital lock-up risk.