Compare
Two to four listings side by side, from what each product's own pages say and the earlier Kairos listing.
Earlier-listing fields are what the Kairos catalogue said at the time, and website metadata can describe a publisher rather than the product. Neither confirms who runs a service, its current price or its regulatory status. Download this comparison as CSV
| Field |  |  |
|---|---|---|
| Product overview | Kalshi operates an event-contract exchange and provides developer interfaces for market data and trading. Its documentation separates prediction contracts from perpetual futures, and its account guide describes age, identity-verification and jurisdiction conditions. | Polymarket provides event-contract markets and developer interfaces for discovery, order books, data and execution. Its international polymarket.com service is separate from Polymarket US; the international site currently directs US visitors to the US product and offers a view-only path. |
| Research classification | Prediction-market products | Prediction-market products |
| Resource type | Product or service | Product or service |
| Platforms named in product context | Kalshi | Polymarket |
| Latest sourced pricing | Kalshi’s help page describes transaction fees that depend on the contract and market. Some markets also charge makers when resting orders execute. The exchange’s current fee schedule and order display govern the applicable charge; a single universal percentage would be misleading. | The current international fee guide describes market-specific taker charges using a price-dependent formula, with makers uncharged. Certain geopolitical/world-event markets are described as fee-free, and combos have a separate rate. Funding intermediaries may charge independently. This is not the Polymarket US fee schedule. |
| Access requirements | The account guide requires users to be at least 18 and complete requested identity checks. International access has jurisdiction restrictions. | Not established |
| Developer access | The exchange documents REST, WebSocket and FIX interfaces, a demo environment and an MCP connector. | The provider publishes separate market-data and trading documentation and links US documentation separately. |
| Product distinction | Prediction-contract and perpetual-futures APIs are documented separately. Their fee and margin rules should not be mixed. | The international website and documentation direct US users to a separate US product. |
| Cost structure | Not established | Fees depend on market category, order role and price; a blanket statement that all Polymarket trades are free would be inaccurate. |
| Capability: Data API | Developer interfaces cover market data and trade execution. | Programmatic access is described in the product overview. |
| Capability: Developer SDK | Not established | A software development kit or language client is described. |
| Capability: MCP tools | The documentation links an assistant connector for market research, portfolio reads and alerts. | Not established |
| Capability: WebSocket delivery | WebSocket interfaces are documented for the exchange products. | Not established |
| Developer and product resources | Pricing: https://help.kalshi.com/en/articles/13823805-fees; About the product: https://help.kalshi.com/en/articles/13823778-signing-up-as-an-individual; Documentation: https://docs.kalshi.com/welcome | Documentation: https://docs.polymarket.com/; About the product: https://polymarket.com/event/anthropic-ipo-by; Pricing: https://docs.polymarket.com/trading/fees |
| Website research check | 2026-11-03T16:55:00.957827+00:00; A dated public product or documentation page was reviewed. This establishes the source of the listed facts, not tested functionality, operating health, security or account eligibility. | 2026-11-03T16:35:44.269945+00:00; A dated public product or documentation page was reviewed. This establishes the source of the listed facts, not tested functionality, operating health, security or account eligibility. |
| Vultax assessment | Not assessed | Not assessed |
| Website | https://kalshi.com/ | https://polymarket.com/ |
| Evidence | View source (opens in a new tab) Observed Full profile | View source (opens in a new tab) Observed Full profile |
Earlier descriptions come from the Kairos catalogue by its contributors, used under CC BY 4.0. Attribution and licences.