arb.x402gate.com offers a focused arbitrage data feed that identifies real‑time cross-market opportunities between Polymarket and Kalshi on the Base network. Its single /opportunities endpoint returns pricing valid at the time of the call for rapid monitoring and automated trading; callers must independently confirm calculations because the provider disclaims warranties and liability. The service is low-cost (USD 0.09 per call) and is designed for bots, alerts, and post-trade analysis.