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Building a Kalshi–Polymarket Arbitrage Bot: Cross-Platform Strategy in 2026

Cross-platform arbitrage between Kalshi and Polymarket remains one of the most reliable edges in prediction markets. When the same event is priced differently across platforms, you can lock in nearly risk-free profit by buying the cheap leg on one and the opposing leg on the other.

Polymarket Trading Bot

Here’s how a production-grade arbitrage bot actually works.

Core Strategy

For any binary event:

  • Compare YES/NO prices on both platforms
  • If YES_Polymarket + NO_Kalshi < 1.00 (or vice versa) after fees → execute the arb

Profit formula (simplified):

gross_spread = 1.0 - (price_a + price_b)
net_profit = gross_spread - fees_polymarket - fees_kalshi - slippage
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Target gross spread ≥ 6–8% to remain profitable after all frictions.

Bot Architecture

1. Dual Data Pipeline

  • Polymarket: CLOB V2 WebSocket + GraphQL for real-time prices and order book
  • Kalshi: REST + WebSocket API for live quotes
  • Event mapping layer (same events often have different IDs across platforms)

2. Opportunity Scanner

  • Continuous loop comparing normalized prices
  • Fee-aware calculator (Polymarket ~2%, Kalshi ~0.7–1.2%)
  • Slippage estimator based on current depth
  • Only trigger when net edge exceeds threshold

3. Atomic Execution

  • Execute slower leg first (usually Kalshi)
  • Immediately hedge on faster platform (Polymarket)
  • Cancel both if one leg fails
  • Use IOC/FOK orders to minimize partial fill risk

4. Risk & Capital Management

  • Max exposure per event
  • Global daily volume and drawdown limits
  • Capital rotation logic (funds locked until resolution)
  • Monitor resolution rule differences between platforms

Key Challenges & Solutions

  • Latency: Polymarket is faster. Solution: low-latency VPS + prioritize slower leg.
  • Capital Lockup: Funds tied on both platforms. Solution: focus on shorter-duration markets and rotate capital efficiently.
  • Fees & Slippage: Can destroy small spreads. Solution: strict minimum edge filter and depth validation.
  • Resolution Risk: UMA disputes on Polymarket. Solution: avoid or hedge high-dispute-probability markets.

Production Tips

  • Run on dedicated low-latency infrastructure
  • Implement comprehensive logging with full decision trace
  • Add circuit breakers for extreme volatility
  • Monitor platform rule changes daily
  • Start with paper trading to validate execution reliability

Cross-platform arbitrage isn’t completely “risk-free,” but with proper engineering it can be one of the lowest-risk, highest-Sharpe strategies available in prediction markets.

The edge exists because of fragmentation between regulated fiat (Kalshi) and crypto-native (Polymarket) platforms. Builders who master synchronization, execution hygiene, and risk modeling are well-positioned to capture it.

If you have more questions, please feel free to contact me at any time: https://t.me/FatherSon97

Tags: #Polymarket #Kalshi #Arbitrage #TradingBots #PredictionMarkets #DeFi #Web3 #CLOB #QuantitativeTrading #Fintech

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