Polymarket API vs Kalshi API
Verdict: Polymarket API: API access free. Kalshi API: API access free. Safety score: Polymarket API 30%, Kalshi API 50%. They differ on assets, live vs paper, order approval, pricing, rate limits; the table below shows each fact with its source.
| Field | Polymarket API | Kalshi API |
|---|---|---|
| Category | Prediction market APIs & agents | Prediction market APIs & agents |
| Assets | prediction markets, perpetual futures via the separate Perps API | prediction markets, perpetual futures (Margin/perps markets) |
| Live vs paper | live only (no testnet); CLOB V2 since Apr 28 2026 | live; separate demo environment with mock funds (demo.kalshi.co) |
| Order approval / safety | wallet-signed orders on the international CLOB (V2 SDKs: py-clob-client-v2, clob-client-v2); separate Polymarket US API with Ed25519 keys and an order preview endpoint; Polymarket's docs now lead with unified SDKs (@polymarket/client for TypeScript; pip install polymarket-client, imported as polymarket, for Python) and call the V2 CLOB clients the previous SDKs; Data API v1 retires on Nov 2, 2026 per Polymarket's migration guide: reads use the /v2 routes (cursor pagination, snake_case fields), and GET /v1/accounting/snapshot retires with v1 with no v2 replacement | official REST and WebSocket Trade API with RSA-PSS or Ed25519 signed keys; demo credentials are separate from production; since Oct 15, registered MCP clients can be granted read access to your portfolio (balances, positions, orders, fills) through a read::mcp_portfolio OAuth grant that cannot execute orders or change funding; since Oct 29, direct members can use subaccount-restricted API keys to move funds between exchange indices within that subaccount (not a withdrawal); Kalshi also runs its own hosted MCP connector (https://api.elections.kalshi.com/mcp; public market tools need no account, portfolio and price-alert tools sign in by OAuth with read::mcp_portfolio, read::mcp_alerts and write::mcp_alerts): it does not place or cancel orders, transfer funds or save trade drafts, its links send you to Kalshi to submit an order yourself, and its only write action is creating and deleting price alerts; no official trading MCP (community MCPs exist) |
| Pricing / free tier | API access free; trading fees vary by market | API access free; exchange trading fees apply per contract |
| Rate limits | per-endpoint limits in docs | token buckets by tier: Basic 200 read / 100 write tokens per second, most requests cost 10 tokens; higher tiers by volume (docs.kalshi.com); since Oct 15 GET /portfolio/balance has its own bucket (Basic and Advanced 1 call/sec, higher tiers 5/sec, no burst): Kalshi suggests reacting to the fills WebSocket instead of polling it |
| Official / community | official | official |
| Last checked | 2026-11-09 | 2026-11-09 |
| Source | docs.polymarket.com | docs.kalshi.com |
| Website | Visit Polymarket API | Visit Kalshi API |
Both are listed under Prediction market APIs & agents, where every tool in the category is shown with the same sourced facts.