Kalshi API vs Polymarket API (CLOB)
Side by side from sourced facts: pricing, markets, custody, incidents and each bot’s rule-based report card. We don’t pick a winner; what fits depends on how you trade.
| Kalshi API | Polymarket API (CLOB) | |
|---|---|---|
| Report card | Caution At least one documented security incident, regulator action (non-fraud) or unverified performance claim in the last 5 years. | Caution At least one documented security incident, regulator action (non-fraud) or unverified performance claim in the last 5 years. |
| Category | Prediction market bots | Prediction market bots |
| What it is | Kalshi's official exchange API (REST, WebSocket and FIX) for automated trading of event contracts, with a demo environment. | Polymarket's official developer APIs and SDKs for market data and placing orders on its order book. |
| Pricing | Not verified yet | Taker fees on some markets, set by the protocol (formula fee = C × feeRate × p × (1 − p)); makers pay no fees; geopolitical and world-events markets are fee-free. Source: docs.polymarket.com/trading/fees.md |
| Markets / exchanges | Kalshi (event contracts) Source: docs.kalshi.com/welcome | Polymarket Source: docs.polymarket.com |
| Your money | Trades through your account on a regulated exchange via its API. | Self-hosted: you run the software and your keys stay on your machine. |
| Code / license | Proprietary (Kalshi Developer Agreement) | Proprietary |
| Facts on record | Mar 4, 2025: the Nevada Gaming Control Board ordered KalshiEX LLC to stop offering sports and election event contracts in Nevada, treating them as unlicensed wagering. Source: gaming.nv.gov/siteassets/content/about/press-release/NGCB_-_News_Release_ | Jan 3, 2022: per the CFTC, Blockratize Inc. d/b/a Polymarket settled charges of offering off-exchange event-based binary options without DCM designation or SEF registration; $1.4M civil penalty and an order to wind down non-compliant markets. Source: cftc.gov/PressRoom/PressReleases/8478-22 |
| Official site | docs.kalshi.com | docs.polymarket.com |
Facts checked Oct 15, 2026. Report cards follow published rules; payouts never change them. Not investment advice.