Prediction markets — Kalshi + Polymarket prices (public APIs)

One normalised row per market from the public, read-only listings of Kalshi and Polymarket: event, market question, category, the current yes/no price (0–1 USD per share, i.e. the market-implied probability), bid/ask, last trade, volume, liquidity, open interest, open/close dates, status and a link. Filter by venue, status, free text, category or Kalshi series ticker.

Market data only, for information. The Actor holds no account at either venue, sends no order, and nothing here is advice or an invitation to wager. Availability of the venues themselves depends on where you are; reuse of the data is governed by the Kalshi and Polymarket terms of service — check them before redistributing.

Data source and status

Kalshi	https://api.elections.kalshi.com/trade-api/v2/events?with_nested_markets=true (status / series filters, cursor paging, 100 events per request). Unauthenticated read access, as documented by Kalshi. The old host trading-api.kalshi.com answers 401 "API has been moved" — this Actor uses the current one
Polymarket	https://gamma-api.polymarket.com/events (active/closed filters, sorted by 24-hour volume, 25 events per request with nested markets and tags) and /public-search?q= when a search text is given. Public Gamma API, no key
Refresh cadence	Live on every run — prices are read at fetch time (fetched_at on each row). Kalshi and Polymarket quotes move continuously; a row is a snapshot, not a feed
Response guards	Every field a row depends on must be present with the type measured on 2026-09-04 (Kalshi *_dollars price strings, *_fp quantities; Polymarket outcomes / outcomePrices JSON strings). Anything else fails the run loudly instead of writing guessed values
Rate	At most one request per request_interval_ms (default 500 ms); back-off on 429/5xx
Identification	User-Agent: RetrainMap-prediction-markets/0.1 (https://apify.com/retrainmap; <contact>) plus the contact address in the standard From: header

Honesty note: Kalshi's API does not return the web-page slug of a market, so the Kalshi url is the API resource for that market (/trade-api/v2/markets/<ticker>), not a kalshi.com page; use series / event_id / market_id to find it on the site. Polymarket rows link to the market page (polymarket.com/event/<event>/<market>).

Input

Field	Type	Meaning
source	both / kalshi / polymarket	Default both (Kalshi gets the first half of the row budget, Polymarket the rest)
status	open / closed / settled / all	Default open = trading now. Polymarket has one closed flag for closed and settled
search	string	Optional. Kalshi: substring match on event/market titles while paging; Polymarket: the venue's own search
category	string	Optional substring. Kalshi event category (Economics, Politics, Sports, …); Polymarket tag label/slug or series
series_ticker	string	Optional, Kalshi only (e.g. KXFED). When set, Polymarket is skipped
max_records	integer	Default 300
request_interval_ms	integer	Default 500 (floor 250)
contact_email	string	Sent in the User-Agent and From: header

Example — Kalshi Fed-rate markets only:

{ "source": "kalshi", "series_ticker": "KXFED", "max_records": 50 }

Output (dataset row)

source, market_id (Kalshi ticker / Polymarket market id), event_id, series, event_title, market_title, market_subtitle, category, tags (Polymarket), market_type, outcomes, outcome_prices, yes_price, no_price (0–1), price_basis (last_trade, midpoint or outcome_prices), yes_bid, yes_ask, no_bid, no_ask, last_price, volume, volume_24h, liquidity, open_interest (Kalshi), open_time, close_time, expiration_time, status (the venue's own value), result (Kalshi, once settled), url, fetched_at.

Kalshi yes_price is the last trade price when the market has traded, otherwise the yes bid/ask midpoint when both sides are quoted, otherwise null; no_price is 1 − yes_price. Polymarket yes_price/no_price are the venue's outcomePrices for the Yes/No outcomes; for markets whose outcomes are not Yes/No the first outcome's price is reported as yes_price and the full outcomes/outcome_prices lists are on the row. Polymarket yes_bid/yes_ask are the venue's best bid/ask for the first outcome; markets without prices (not yet deployed) are skipped and counted in the run summary. A run summary (counts per venue, filters, request count) is stored as RUN_SUMMARY in the run's key-value store.

Pricing (pay per event)

Event	Price
run-start — once per run	$0.10
record — per row written	$0.005

The default run (300 rows) costs $1.60. Rows stop when your run's maximum charge is reached; the run summary says so.

Operator

Steelyard Ventures LLC (RetrainMap) — info@steelyardclinical.com. The Actor writes only to its own dataset and key-value store; it stores no credentials and sends nothing but GET requests.