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Kalshi vs Polymarket (2026): regulation, fees, liquidity, API

If you trade event contracts seriously in 2026, the decision is rarely "Kalshi or Polymarket" — it's "which one for this trade." The two venues list heavily overlapping events but differ in almost every structural way that matters: who regulates them, how positions settle, what trading costs, how deep the books are, and what integrating them feels like. This page is the head-to-head.

At a glance

Regulation and settlement

Kalshi operates as a CFTC-regulated exchange in the United States. You open an account with KYC, deposit US dollars, and your positions and balances sit at the exchange like a brokerage. Contract terms and resolution rules go through a regulated listing process, and disputes have a formal, regulated path. For US-based traders and funds with compliance requirements, this is usually the deciding factor on its own.

Polymarket is crypto-native. You hold USDC in a wallet on Polygon, and trades settle on-chain: each market outcome is an ERC-1155 token, and a fill is a token transfer. Resolution is handled through Polymarket's oracle process rather than a regulated exchange rulebook. Custody works differently too — the venue never holds your funds the way a brokerage does, but you (or your bot) are responsible for a private key, which is its own operational risk. Access rules and geographic availability have shifted over time for both venues, so check the current terms for your jurisdiction before wiring anything up.

Neither model is strictly better. Regulated settlement buys you legal clarity; on-chain settlement buys you self-custody and composability. What they cost you is symmetric: Kalshi constrains who can trade and how, while Polymarket pushes key management and chain mechanics onto you — a real burden once software holds the keys (see agent custody).

Market coverage

Coverage overlaps heavily on the biggest categories — elections, economics (Fed decisions, CPI), and major sports and awards — and this overlap is exactly where cross-venue price comparison pays. Beyond the overlap, each venue has a long tail the other lacks: Kalshi lists a deep bench of recurring, data-settled economic and weather series that suit systematic strategies, while Polymarket's crypto-native audience produces markets on crypto prices and internet-culture events that Kalshi typically doesn't list. Exact coverage shifts weekly, so treat any static list as stale — the structural point is that the same real-world event frequently trades on both, under two unrelated identifiers (a Kalshi ticker vs a Polymarket condition ID). Matching them is manual work unless you use a unified market ID layer.

Fees

This is where displayed prices mislead.

Kalshi charges an explicit taker fee: 0.07 × contracts × price × (1 − price) with price in dollars, rounded up to the next cent. It peaks at 50¢ (1.75¢ per contract) and shrinks toward the tails; resting orders that provide liquidity generally pay no trading fee on most markets. Polymarket charges no exchange trading fee on most markets — but the spread you cross, the price impact in a thin book, and Polygon gas on settlement are real costs that never show up as a line item.

The practical consequence: a market showing 47¢ on Kalshi and 46.5¢ on Polymarket is not automatically cheaper on Polymarket. Whether it is depends on the Kalshi fee at that price, the depth behind Polymarket's displayed quote, and your size. The full worked comparison lives at Kalshi vs Polymarket fees, with per-price breakdowns in Kalshi fees explained and Polymarket fees and gas explained.

Liquidity and microstructure

Both venues run central limit order books, but the books behave differently. Liquidity is event-driven and concentrated on both: headline markets can be tight and deep, while the long tail is thin enough that a modest market order moves the price several cents. As a rough tendency, each venue is deepest in its home turf — Kalshi in its recurring data-settled series, Polymarket in the large political and crypto markets its audience gravitates to — but depth shifts with the news cycle, so measure the actual book rather than trusting a reputation.

Microstructure details differ too. Kalshi's cent tick on a 1–99¢ scale means the minimum spread is a full cent — material on cheap contracts. Polymarket's decimal pricing and token mechanics create their own quirks, including the fact that buying NO is trading a separate token rather than selling YES. For how thin books punish naive orders on either venue, see slippage in thin prediction markets and execution quality.

API and developer experience

The APIs share almost nothing.

Kalshi looks like a classic exchange API: REST + WebSocket at api.elections.kalshi.com/trade-api/v2, API-key request signing, JSON orders against human-readable tickers, prices as integer cents. Polymarket splits across Gamma (gamma-api.polymarket.com, metadata, no auth) and the CLOB (clob.polymarket.com), where orders are EIP-712 typed-data messages signed by a wallet key, matched off-chain, and settled on Polygon. Different auth, different ID schemes, different price formats, different failure semantics. The full teardown is at Kalshi API vs Polymarket API, and each venue has a hands-on guide: Kalshi, Polymarket.

Verdict, by who you are

The honest verdict is that for most serious traders the answer is both, and the real cost is the integration: two auth models, two ID schemes, two fee models, two sets of failure modes. That's the problem Mithril exists to remove — one API and hosted MCP server across both venues, with fee-aware routing that compares net prices per order. Or build both integrations yourself; the prediction market API guide covers what that takes.

Venue rules, fees, and coverage change. Details above reflect public documentation as of July 2026 — always confirm against the venues' own docs before trading real money.