Kalshi API & Developers
Kalshi provides a documented API stack for market data, private account actions, and trading workflows. For developers, the key questions are access level, signing flow, rate limits, and whether you need REST, websockets, or FIX.
1. REST and WebSocket Protocols
Kalshi offers two distinct methods for interfacing with their central limit order book (CLOB).
- REST API: Useful for standard requests such as market data, account state, and certain trading actions.
- WebSocket API: Useful when you need streaming updates instead of repeated polling.
2. API Authentication (RSA-PSS)
Kalshi uses a signature-based authentication model for protected API actions.
Kalshi documents RSA-PSS request signing in its developer docs. That is the part most developers should get working through the official SDK or a carefully tested client instead of building from memory.
To authenticate:
- Developers must digitally sign a unique timestamp utilizing their private RSA key.
- Kalshi verifies the signature against the public key uploaded to the dashboard.
- Developers then use the authenticated flow documented by Kalshi for protected requests and websocket access.
3. The Four Access Tiers
Kalshi documents multiple API access tiers with different read and write limits.
Basic Tier
Entry-level access with lower limits. Good for initial development and light usage.
Advanced Tier
Higher limits and broader live access for users who meet the platform's documented requirements.
Premier Tier
Higher-volume access with more generous limits for qualifying participants.
Prime Tier (Institutional)
The highest documented tier, intended for more demanding production workflows. Kalshi also documents FIX support separately for firms that need it.
Rate Limits
Kalshi documents rate limits by tier. Developers should treat those limits as part of system design, not as a footnote.
That means:
- watch rate-limit headers
- design retry logic carefully
- avoid bursty polling when a websocket would be better
- assume limits and tier rules can change over time
FAQ
Does every developer need FIX?
No. Most developers should start with REST and websockets. FIX is a specialized workflow for teams that actually need it.
Should I hardcode assumptions about tier approval?
No. Access tiers and requirements should be checked against Kalshi's current docs.
What should I read next?
Read Kalshi API Guide, Kalshi Overview, and Prediction Market Data Analytics.