Kalshi vs Polymarket (2026): Fees, Access, APIs and Bots Compared

"Kalshi or Polymarket?" used to be a simple question: Kalshi for Americans, Polymarket for everyone else. In 2026 there are really three venues to compare: Kalshi, Polymarket's original international exchange (polymarket.com), and Polymarket US, a separate CFTC-regulated exchange with its own app, fees and API.

This guide compares them on what matters most: who can use each one, what trades cost, how markets settle, who holds your money, and how well each suits automated trading. Facts are checked against each venue's own documentation as of October 8, 2026. Fees and eligibility change often, so confirm before you trade.

The short answer

• Where you are decides most of it. US residents can use Kalshi or Polymarket US, subject to state restrictions. They can't trade on Polymarket's international exchange. Many other countries can use Polymarket international or Kalshi, but each has its own restricted list.
• Fees are close. Kalshi and Polymarket US use nearly the same formula. Polymarket international is cheaper in most non-crypto categories and free in geopolitics.
• For bots and copy trading, Polymarket international is the most open: public order book, onchain positions anyone can look up, and self-custody. Kalshi has the most mature traditional API (REST, WebSocket, FIX, a demo environment), but you can't see other traders' accounts.

Side-by-side comparison

	Kalshi	Polymarket (international)	Polymarket US
Regulator / model	CFTC-designated contract market	Crypto exchange with an onchain settlement layer; not open to US users	CFTC-designated contract market (formerly QCX), clearing via Polymarket Clearing
Who can use it	US (minus some states) and many countries, excluding a restricted list in its Member Agreement	Most countries, excluding a published restricted list that includes the US	Eligible US residents in most states
Account	KYC account	Crypto wallet (self-custody)	KYC account in a mobile app
Money	USD (ACH, card, wire); international users card, wire or crypto	pUSD, a USDC-backed token on Polygon	USD (card, ACH, Apple Pay, PayPal, Venmo, USDC, wire)
Taker fee	0.07 × C × P × (1 − P), rounded up; some series lower	Category rate × C × p × (1 − p): 0.04–0.07, geopolitics 0	0.0695 × C × P × (1 − P)
Maker fee	Lower (0.0175) or zero, by market	Zero, plus a share of a rebate pool	Rebate
Settlement	Kalshi determines outcomes per contract rules	UMA optimistic oracle; Chainlink for short crypto markets	Exchange resolution per contract rules
API	REST, WebSocket, FIX, official Python/TypeScript SDKs, demo environment	Public REST + WebSocket, unified Python SDK, wallet-signed orders	REST API and SDKs (polymarket-us) via a developer portal after KYC
Can you see other traders' positions?	No	Yes, positions and trades are public by wallet address	No public wallet layer

Sources: Kalshi fee schedule, Kalshi API docs, Kalshi international help, Polymarket fees, Polymarket geographic restrictions, Polymarket US docs, and DeFi Rate's October 2, 2026 fee comparison.

Access: start here

Kalshi

Kalshi is a CFTC-regulated exchange. In the US, as of early October 2026, RotoGrinders lists it as unavailable in nine states (AZ, IL, MA, MD, MI, MT, NV, OH and WA) amid ongoing state-level legal disputes over sports contracts (RotoGrinders, Oct 2026). Kalshi also accepts users from "many countries" outside the US, subject to a restricted-country list in its Member Agreement. International users fund by card, wire or crypto rather than ACH (Kalshi Help Center).

Polymarket international

polymarket.com blocks or restricts trading in a published list of jurisdictions. The United States is on it, along with the UK, France, Germany, Italy, Australia, Singapore, Thailand, Taiwan, several Canadian provinces and others (Polymarket docs). Polymarket's terms prohibit using a VPN to get around this. Our Polymarket legality and geo-restrictions guide has the full list and what it means.

Polymarket US

Polymarket acquired QCEX in 2025 and now runs Polymarket US, a CFTC-regulated exchange with a mobile app, KYC and dollar balances. As of October 2026, RotoGrinders reports it's open to eligible users without a waitlist and excluded in the same nine states as Kalshi. It's a different exchange from polymarket.com, with different markets, fees, rules and API. A wallet or bot built for one doesn't work on the other.

Fees, with worked examples

All three use a formula that peaks at 50¢ and shrinks toward 1¢ and 99¢. Here's what $100 of contracts at 50¢ (200 contracts), taker, held to settlement costs on each (our calculation from the published formulas):

Venue	Rate	Fee
Kalshi (standard)	0.07	$3.50
Polymarket US	0.0695	$3.48
Polymarket international – crypto	0.07	$3.50
Polymarket international – sports, economics, culture, weather	0.05	$2.50
Polymarket international – politics, finance, tech, mentions	0.04	$2.00
Polymarket international – geopolitics	0	$0.00

For makers, Kalshi charges a reduced rate (0.0175) or nothing depending on the market, Polymarket US pays a rebate, and Polymarket international charges nothing and shares a portion of taker fees with makers. Selling before settlement costs a second fee on all three. More detail: Polymarket fees explained.

Two practical notes:

• Rounding. Kalshi rounds fees up to the cent per fill but tracks the overpayment across an order and refunds it (Kalshi docs). On tiny orders, check the fee preview.
• Funding costs can outweigh trading fees. Card deposits on US apps can cost 2–3.5% (DeFi Rate). On Polymarket international, getting pUSD onto Polygon has its own exchange and bridge costs.

Settlement and resolution

Kalshi determines outcomes from the source named in each contract's rules and settles automatically: $1 per winning contract, with no settlement fee for simple yes/no markets (Kalshi docs).

Polymarket international uses the UMA Optimistic Oracle. Anyone can propose an outcome with a bond, there's a challenge window, and disputed outcomes can escalate to a UMA token-holder vote. Short-term crypto markets settle automatically from Chainlink data. Winners redeem shares onchain. See how Polymarket markets resolve.

Polymarket US resolves under its exchange rulebook and settles through its clearinghouse, in line with other CFTC-regulated venues.

What matters for traders: on Polymarket international, rule wording and the dispute process carry more weight, because outcomes are decided by an open proposal-and-challenge system rather than by an exchange's own staff.

Custody and counterparty risk

• Kalshi and Polymarket US hold your dollars in a regulated account structure. You rely on the exchange and clearinghouse.
• Polymarket international is self-custodial: funds sit in your own wallet and positions are tokens you control. You don't rely on an exchange to hold your balance, but you're fully responsible for key security. Lose the key and the funds are gone. Let someone else hold it, and you're trusting them completely (see bot security).

APIs and bots

Kalshi

Kalshi's API is the most "traditional finance" of the three. It offers REST, WebSocket and FIX, official Python and TypeScript SDKs, tiered rate limits, order groups that auto-cancel past a contract limit, and a demo environment with mock funds for testing. Authentication uses an API key pair (Ed25519 or RSA-PSS) that signs each request (Kalshi API keys, demo).

Polymarket international

Polymarket's market data is public with no key needed: the Gamma API for discovery, the CLOB for order books, a Data API for positions and trades, and WebSockets for live updates. Orders are signed by your wallet. A unified Python SDK covers all of it. Because every position lives onchain, you can look up any wallet's trades, positions and P&L, which is what makes copy trading possible. There's no demo environment, so bot builders usually test with paper trading against the live book. Start with our Python API guide.

Polymarket US

Polymarket US provides API keys through a developer portal once your account is verified, plus SDKs (pip install polymarket-us / npm install polymarket-us) (quickstart). It's a KYC'd, account-based API like Kalshi's, not the wallet-based CLOB of the international exchange.

Bottom line for automation

Goal	Best fit
Copy trading specific wallets	Polymarket international (public onchain data)
Testing with fake money in a sandbox	Kalshi (demo environment)
Institutional-style connectivity (FIX)	Kalshi
Short-dated crypto markets every 5–15 minutes	Polymarket international (details)
Lowest fees in politics/sports	Polymarket international (where available)
US resident wanting a regulated venue	Kalshi or Polymarket US

Cross-venue arbitrage

Prices for the same event sometimes differ between Kalshi and Polymarket, and "Kalshi–Polymarket arbitrage" is a popular search. In practice:

1. Few people can legally hold accounts on both Kalshi and Polymarket international: US residents are excluded from the latter, and many non-US users from the former.
2. Resolution wording differs. Two markets that look identical can resolve differently on edge cases, and that's how a "hedge" becomes two losses.
3. Capital sits on both sides until settlement, and fees apply on each venue.

See Polymarket arbitrage explained for what is and isn't a real arbitrage.

Which should you use?

• You're in the US: Kalshi or Polymarket US (if your state allows). Compare prices on the specific market. Many traders keep both.
• You're outside the US, in a country not on Polymarket's restricted list: Polymarket international has the deepest crypto-native markets, lower fees in most categories and fully public data. Kalshi may also be available to you. Check its Member Agreement.
• You want to automate: pick the venue first, then the tooling. Kalshi suits FIX/REST shops that want a sandbox. Polymarket international suits copy trading and onchain analytics.

FAQ

Is Kalshi cheaper than Polymarket? Against Polymarket US, they're nearly identical (0.07 vs 0.0695). Against Polymarket international, Kalshi is the same in crypto and more expensive in sports, politics and geopolitics.

Can I copy trade on Kalshi? Not in the way you can on Polymarket. Kalshi accounts aren't public, so you can't follow a specific trader's positions from public data.

Are Polymarket and Polymarket US the same? No. They're separate exchanges with different eligibility, markets, fees and APIs.

Does Ghost Trader work on Kalshi or Polymarket US? No. Ghost Trader trades only on Polymarket's international exchange, and only where Polymarket allows trading.

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Ghost Trader is a copy-trading and crypto-signal bot for Polymarket's international exchange. Your key stays on your machine, a hosted dashboard sends Telegram alerts, and fractional Kelly sizing runs under a daily-loss kill switch. $199/month, paper mode included. See pricing.

Not financial advice. Trading can lose money. Ghost Trader isn't available where Polymarket restricts trading, including the US, and is not affiliated with Polymarket, Polymarket US or Kalshi.