Kalshi gives away months of history. Here is what is in it

A field note on what Kalshi's public API serves free, checked on 29 September 2026.

This lab started recording Kalshi's order books in July on the theory that whoever holds the history owns something. A reader on r/Kalshi pointed out that a large part of it is given away. They were right. Here is what the free, unauthenticated API returns, with the exact calls.

The base is https://external-api.kalshi.com/trade-api/v2/. No key, no login.

Every market a series has ever listed

GET /historical/markets?series_ticker=KXBTC15M&limit=1000

Pages by cursor. For the Bitcoin fifteen minute series that is 21,560 markets back to 10 December 2025, each with its open, close, result and settlement fields. The ordinary /markets endpoint only reaches back about two months. The historical one continues where it stops.

The trade tape, per market

GET /historical/trades?ticker=KXBTC15M-26JUL301945-45&limit=1000

Needs a full market ticker, not a series. Each trade carries the price on both sides, the contract count, the taker's side, and a timestamp to the microsecond. A busy fifteen minute market runs to several pages.

One minute candles, with open interest

GET /historical/markets/{ticker}/candlesticks?start_ts=...&end_ts=...&period_interval=1

Timestamps are Unix seconds. Each candle has open, high, low, close and mean for the last trade price, the same four for the yes bid and the yes ask, volume, and open interest at the close of the minute. The bid and ask columns are the part most people miss: a one minute picture of the spread, free, for every market back to last December.

What is not there

Depth. There is no historical order book; the obvious URL returns 404. If you want to know how many contracts were resting at each price, you have to be connected to the websocket when it happens and write it down. That is the only part of our archive that could not be rebuilt from this API, and it is the part our depth study depends on.

What this changes

Backtests can start in December, not July. A calibration study on longshots, or on the whale following idea, can be rerun on nine months of settled markets rather than a few weeks. We did not know that in August and it changed our plans.

It also cuts the ground from under one idea we had, which was selling the recorded feed. Kalshi's terms forbid redistributing market data anyway, and most of it is free. What is worth anything is the analysis, which is what this publication sells.

One trap before you start: the time inside a ticker is Eastern, not UTC. That is its own note.