> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gammaflip.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Historical data

> Stored GEX snapshots: levels time series, per-strike snapshots and daily bulk files

GammaFlip stores a GEX snapshot every 15 minutes for every tracked symbol. The
history endpoints give you three ways to read that archive.

| You want | Use | Cost |
| - | - | - |
| How the levels (flip, walls, totals) moved over time | [`/history/levels`](/api-reference/history-levels) | 1 request |
| The capture times of one day | [`/history/timestamps`](/api-reference/history-timestamps) | 1 request |
| The full per-strike picture at one moment | [`/history/snapshot`](/api-reference/history-snapshot) | 1 request |
| What history exists for each symbol | [`/history/coverage`](/api-reference/history-coverage) | Free |
| Bulk CSV files for backtests and spreadsheets | [`/history/files`](/api-reference/history-files) | 1 request for the listing, 1 file credit per download |

Field definitions are in the [data dictionary](/data-dictionary), including the
exact columns of the three daily files.

## Exchanges

History is kept for `bybit`, `deribit`, `okx`, `derive`, `combined` (all crypto
venues merged) and `tradfi`. As everywhere else in the API, `all` / `combined`
with a TradFi ticker resolve to `tradfi`.

<Warning>
  **Venue subsets such as `deribit+derive` have no history.** They are not stored,
  so the history endpoints answer `400 history_not_available` with
  `valid_exchanges`. Per-strike GEX can be summed client-side from single-venue
  data; the gamma flip cannot. The same applies to `?compare=` on
  [`/levels`](/api-reference/levels).
</Warning>

## Session date

Every row carries a `session_date`:

* **Crypto**: the UTC calendar date.
* **TradFi**: the US trading date, the America/New\_York calendar date.

A session counts as **complete** 15 minutes after midnight UTC (crypto) or 30
minutes after the market close (TradFi; early closes are honoured). Daily files
are published once a session is complete.

## Close

`type` is `close` for the **last capture of a completed session**. Every other
row is `intraday`, including the last capture of a session that is still open.
A row can therefore change from `intraday` to `close` after the fact, because
`type` describes the session, not the capture.

## Point-in-time, no look-ahead

Each row is the data as it was captured at `timestamp_utc`. Rows are never
rewritten with later data, which is what a backtest needs.

For TradFi the open interest of a session is published after that session, so
a row captured on session D (including its close) uses the open interest of
the previous session. `oi_date` tells you which session's open interest the row
used. For crypto, open interest is live and `oi_date` equals `session_date`.

## What is in a snapshot

* Every capture has a `TOTAL` snapshot (all expirations combined) and one
  snapshot per expiration. `/history/levels` returns `TOTAL` only;
  `/history/snapshot` and the `levels` and `strikes_by_expiry` files also cover
  single expirations.
* Per-strike data covers strikes within +/- 25% of that snapshot's spot.
* Timestamps are ISO 8601 UTC with `Z` and second precision. Expirations are
  ISO `YYYY-MM-DD` or `TOTAL`.
* All GEX values are USD per 1% move of the underlying. `call_gex` and
  `put_gex` are non-negative; `net_gex = call_gex - put_gex`.
* `schema_version` is `1` today. Existing columns will not change meaning
  within a version.

## Not available

* **Volume** is not captured. There are no volume columns.
* **Venue subsets** (see above).
* Snapshots from before open interest was stored have empty `call_oi` / `put_oi`
  columns.

Use [`/history/coverage`](/api-reference/history-coverage) to see where each
symbol's history starts.

## Quotas

The query endpoints cost one request from your daily quota. File downloads use
a separate daily bucket of file credits, so a bulk download never eats your
request quota. See [Rate limits](/rate-limits#history-file-credits).


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