# Polymarket US API A keyless public gateway for reading, and a signed key behind KYC for trading. *https://predictionmarkets.tools/tools/polymarket-us-api · Prediction Market Data APIs* ## Facts ### At a glance | Field | Value | | --- | --- | | Vendor | Polymarket | | Category | Prediction Market Data APIs | | Job | realtime | | Website | https://polymarket.us | | Pricing model | commission | | Free tier | true | | Open source | false | | Licence | none | | Self-hosted | false | | Tested hands-on | false | | Last updated | 2026-09-19 | ### Availability | Field | Value | | --- | --- | | Jurisdictions | us | | Open to US persons | true | | KYC required | true | ### Markets | Field | Value | | --- | --- | | Subjects | politics, sports, macro, crypto, science, culture, business | | Settlement | cash | | Resolved by | The exchange itself. Polymarket US determines each contract under the rules of its series, and the public API exposes the outcome as a settlement price per market slug rather than as an oracle record. | ### Economics | Field | Value | | --- | --- | | Taker fee | 1.74 | | Maker fee | -0.31 | | Liquidity model | clob | | Platforms | library | | AI features | none | ### Interfaces | Field | Value | | --- | --- | | API | true | | WebSocket | true | | Scripting | none | | Python | true | | MCP server | false | | Export | json | ### Capabilities Yes: order_book, automation, live_trading, portfolio_tracking No: charting, screening, backtesting, paper_trading, calibration_scoring, cross_venue, alerts, news, tax_reporting *Verified: pricing 2026-09-19; availability 2026-09-19.* ## What it is The developer surface of Polymarket's US exchange, split across two hosts that behave nothing alike. `gateway.polymarket.us` is the public half and takes no credentials at all. It serves markets, events, series, tags, sports leagues and teams, full-text search, price history, best bid and offer, the order book and the settlement price — everything a reader, a screen or a chart needs. Its generated OpenAPI description carries an explicit empty `security` list, and on 19 September 2026 every one of those paths answered this machine with 200 and no headers. `api.polymarket.us` is the authenticated half: orders, portfolio, balances, and two WebSockets — a private stream for order, position and balance updates, and a markets stream for books and trades. An unauthenticated request to its root answers `401 Missing required API key headers`. Two things here have no counterpart on the international platform. **Combos** are multi-leg instruments you create through the API — up to 1,000 new combo instruments per exchange participant per week, resetting Monday at 00:00 UTC, with returning an existing canonical combo not counting against the quota. And an **RFQ layer** sits beside the book for those combos: create a request, read quotes, accept one side, confirm during last look. There is also a separate institutional track — a Trader Guide with private-key JWT registration, preprod and production environments, and drop-copy reporting — documented alongside the retail one. ## Availability This is the CFTC-designated US exchange, so the account side is as narrow as the venue's: an account is opened in the iOS app, identity verification comes before trading and before API access, and an invite code may be required. The key is then created at the developer portal by signing in with the same method used in the app — the documentation warns that switching between Apple, Google and email sign-in can break key access. The data side carries none of that. The public gateway is a single global host with no region selection, and it answered without credentials. As everywhere in this category, being able to read the book is not permission to trade against it. ## Pricing Nothing is charged for the API itself, on either host. What costs money is the fill, and the fee schedule is the venue's: on this card it is recorded as the effective rate at a price of 50 cents, where the taker pays 1.74% of the dollar of payout and the resting side is **paid** 0.31% rather than charged. That maker figure is a rebate, which is why it is negative here — read the fee page and the [Polymarket US](https://predictionmarkets.tools/tools/polymarket-us) card for the full curve before planning around the midpoint number. There are no data plans, no tiers and no metering. The ceiling is the rate limit: 20 requests a second per API key across all authenticated endpoints, and 20 a second per IP on the public ones, both answering 429 when exceeded. ## Markets & resolution Sports, overwhelmingly. Paging the public markets endpoint 500 rows at a time with `active=true&closed=false` reached 60,000 rows on 19 September 2026 without running out, and 52,800 of those carried `category: sports` against 6,351 politics, 472 culture, 151 macro, 79 technology, 77 finance, 54 crypto, 9 geopolitics and 7 science. Most of the sports volume is derivative lines rather than distinct questions — quarter totals, spreads and alternate handicaps on the same fixture, each its own row with its own slug. Resolution is the exchange's own. There is no oracle, no bond and no dispute window to model: the outcome arrives as a settlement price on the market's slug, and a Contract Outcome Review under the rulebook is final. For code, that means the interesting endpoint is `/v1/markets/{slug}/settlement` rather than anything resembling a proposal feed. Identifiers are slug-first. Price history, best bid and offer, the book and the settlement price are all addressed by market slug rather than by numeric id, and the slugs encode the fixture — `aec-nfl-lac-ten-2025-11-02`. Partner external ids (an OpticOdds fixture, for instance) resolve to an internal event through a dedicated endpoint, which is the supported way to join against an outside sports feed. ## Integrations REST on both hosts, plus the two WebSockets. Raw authenticated requests carry three headers — `X-PM-Access-Key`, `X-PM-Timestamp` and `X-PM-Signature` — with the signature built from the timestamp and the request using the secret key. First-party SDKs exist in TypeScript and Python and handle the signing. Both are published by the vendor's own organisation and are MIT-licensed: `polymarket-us` on npm at 0.1.1, last published 21 January 2026 from `Polymarket/polymarket-us-typescript`, and `polymarket-us` on PyPI at 0.1.2, uploaded 22 January 2026 from `Polymarket/polymarket-us-python`, whose default branch was last pushed to on 17 September 2026. Those are 0.x version numbers on a live exchange; pin them. Batch routes take up to 20 orders for create, cancel and modify. The documentation is unusually blunt about what a 200 on those means: a per-entry exchange outcome is delivered on the order stream, not in the response, and `canceledOrderIds` is an echo of the request rather than a confirmation. ## Limitations - **Unknown query parameters are silently ignored.** `/v1/markets?category=politics` returned a response byte-identical to `/v1/markets` on 19 September 2026 — same MD5 — because `category` is not a parameter of that endpoint. A mistyped filter does not 400; it returns an unfiltered page that looks filtered. - **No total count anywhere.** The markets response is a bare `markets` array with no pagination envelope, so there is no way to know how many rows a filter matched without walking to the end. - **`limit` is capped at 500** and silently clamped: a request for 1,000 returns 500 without saying so. - **The developer path runs through an iOS app and an identity check.** No app, no key — and that is the gate on the WebSockets and on every write, not just on trading. - **A latency reject looks exactly like a rate limit.** The five-second order stopgap returns `Global Rate Limit Exceeded`, and backing off in response is the wrong reaction. - **Nothing ports from the international platform.** Different hosts, different identifiers, different signing scheme, no wallet, no UMA. ## Alternatives For the international Polymarket, the [Gamma API](https://predictionmarkets.tools/tools/polymarket-gamma-api) is the catalogue and the [CLOB API](https://predictionmarkets.tools/tools/polymarket-clob-api) is the book and the order router, both keyless to read and neither usable from the US. For the other US-regulated exchange, the [Kalshi API](https://predictionmarkets.tools/tools/kalshi-api) has published token-bucket limits and a demo environment, which this one does not. If the requirement is the same data alongside other venues in one schema, [FinFeedAPI](https://predictionmarkets.tools/tools/finfeedapi) and [Adjacent](https://predictionmarkets.tools/tools/adjacent) sell that, and neither is free. ## FAQ ### Do I need an API key to read Polymarket US market data? No. The public gateway at gateway.polymarket.us answers unauthenticated requests for markets, events, series, sports, search, best bid and offer, the order book and the settlement price. Its OpenAPI description declares an empty security list, and every one of those paths returned 200 without headers on 19 September 2026. ### How do I get a Polymarket US API key? Through the app, not the website. You install the iOS app, create an account, pass identity verification, then sign in at the developer portal with the same method and create a key, which yields a Key ID and a secret shown once. There is no developer path that skips the app or the identity check. ### What are the rate limits? Twenty requests a second per API key on the authenticated endpoints and twenty a second per IP on the public ones. Exceeding either returns HTTP 429. ### Why did my order get rejected with a rate-limit message when I was not near the limit? Polymarket US applies a five-second stopgap to inbound orders during high latency and rejects anything not processed in time. The documentation states that these rejects carry the message about a global rate limit but are not one, and that you should not throttle in response. Standalone cancels are exempt. ### Is this the same API as Polymarket's CLOB and Gamma APIs? No. This is the US exchange operated by QCX LLC — different hosts, different identifiers, different auth, dollar settlement and no on-chain oracle. Code written against the international platform does not port. ## Also from Polymarket - [Polymarket CLI](https://predictionmarkets.tools/tools/polymarket-cli.md) - [polymarket-client](https://predictionmarkets.tools/tools/polymarket-client.md) - [Polymarket CLOB API](https://predictionmarkets.tools/tools/polymarket-clob-api.md) - [Polymarket Gamma API](https://predictionmarkets.tools/tools/polymarket-gamma-api.md) - [Polymarket US Python SDK](https://predictionmarkets.tools/tools/polymarket-us-python.md) - [Polymarket US TypeScript SDK](https://predictionmarkets.tools/tools/polymarket-us-typescript.md) - [Polymarket US](https://predictionmarkets.tools/tools/polymarket-us.md) - [Polymarket](https://predictionmarkets.tools/tools/polymarket.md) - [py-clob-client](https://predictionmarkets.tools/tools/py-clob-client.md) ## Background - [Where weather data comes from and what you may do with it](https://predictionmarkets.tools/guides/where-weather-data-comes-from.md) — Observations, model output and archives are three products with three licences. The forecast is the cheap half; a clean observation history is not. - [Why the same contract costs two different prices on two venues](https://predictionmarkets.tools/guides/why-the-same-contract-costs-two-prices.md) — Two venues quoting one outcome are quoting two contracts. What the gap between the prices is made of - rules, fallbacks, fees, collateral, exits, eligibility. - [What a trade actually costs on a prediction market](https://predictionmarkets.tools/guides/what-a-trade-actually-costs.md) — Venues publish trading fees in four incompatible units, so 3.00% on one can be cheaper than 1.75% on another. How to convert them, and what else takes a cut. ## Also worth comparing - [Kalshi API](https://predictionmarkets.tools/tools/kalshi-api.md) — REST, WebSocket and FIX access to a CFTC-regulated event exchange. - [Futuur API](https://predictionmarkets.tools/tools/futuur-api.md) — One question, two order books — play money and real money, selected per request. - [Limitless API](https://predictionmarkets.tools/tools/limitless-api.md) — REST and WebSocket for markets, books, candles and trading on Base. - [Manifold API](https://predictionmarkets.tools/tools/manifold-api.md) — Every read is keyless, the server is MIT-licensed, and the currency is play money. - [Adjacent](https://predictionmarkets.tools/tools/adjacent.md) — Prediction-market indices and reference rates, with Kalshi on the tier you can test. - [Apify prediction-market scrapers](https://predictionmarkets.tools/tools/apify-prediction-market-scrapers.md) — A store of third-party actors that normalize Kalshi and Polymarket into one row shape.