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

# OPEX calendar

> Daily, weekly, monthly, quarterly — and why anchor expirations matter

**OPEX** (options expiration) is the day options contracts expire. In
crypto, contracts expire on multiple cadences:

* **Daily expirations** — BTC and ETH have daily 0DTE contracts on Deribit
* **Weekly expirations** — every Friday, smaller OI
* **Monthly expirations** — the **last Friday** of each month, much larger OI
* **Quarterly expirations** — last Friday of March, June, September, December — the heaviest of all

The monthly and quarterly expirations are **anchor expiries** —
institutional positioning concentrates in them, GEX clusters around
their strikes, and they often dictate price action in the days leading
up to expiry.

## Why this distinction matters

Monthly/quarterly expirations have:

* **5–10× the OI** of weeklies in the same week
* **Roll activity** in the 3–5 days before — rolling positions to the
  next expiry can move spot
* **Pin risk** from large dealer hedges unwinding on expiry day
* **Vol regime shifts** as the GEX picture redistributes after the
  expiry-day delta unwind

Weekly expirations matter for short-term gamma but have nowhere near
the institutional weight.

## The classification BackQuant returns

Every expiration in our responses comes pre-classified with a `type`
field — you don't have to parse Deribit-style tokens or detect
last-Friday-of-month rules client-side:

| Type        | Definition                           | Example                                                                           |
| ----------- | ------------------------------------ | --------------------------------------------------------------------------------- |
| `quarterly` | Last Friday of Mar / Jun / Sep / Dec | `28MAR25`, `27JUN25`, `26SEP25`, `26DEC25`                                        |
| `monthly`   | Last Friday of any other month       | `25APR25` (April 30 is Wednesday → last Friday is the 25th), `30MAY25`, `25JUL25` |
| `weekly`    | Any other Friday                     | `07MAR25`, `14MAR25`, `21MAR25`, `04APR25`, `11APR25`                             |
| `daily`     | Any non-Friday weekday               | `26MAR25` (Wednesday), `27MAR25` (Thursday)                                       |

`is_anchor: true` is shorthand for `monthly` or `quarterly` — the two
that institutions watch.

Tokens that don't parse cleanly are returned as `unknown` and never
silently filtered out.

## The `/v2/options/opex` endpoint

[`/v2/options/opex`](/api/v2/options/opex) bundles everything you need
for an OPEX-day workflow into one call:

```bash theme={null}
curl "https://api.backquant.com/v2/options/opex?symbol=BTCUSDT&horizon=30" \
  -H "X-API-Key: YOUR_API_KEY"
```

For each upcoming expiration within the horizon, you get:

* **Identification**: token, ISO date, DTE, type, `is_anchor` flag
* **OI block**: `call_oi`, `put_oi`, `total_oi`, `pcr`, **`notional_oi_usd`** (= total\_oi × spot)
* **IV block**: `atm_iv`, `skew_25d`, `put_25d_iv`, `call_25d_iv`
* **Gamma block**: `net_gex`, `call_resistance`, `put_support` (computed per-expiry from the strike × expiry heatmap), `max_pain`

Plus a `next_anchor` pointer at the closest monthly/quarterly so you
can highlight it in your UI.

## Filtering for the institutional view

Want only the heavyweight expirations? Filter to anchors:

```bash theme={null}
curl "https://api.backquant.com/v2/options/opex?\
symbol=BTCUSDT\
&horizon=90\
&types=monthly,quarterly" \
  -H "X-API-Key: YOUR_API_KEY"
```

You'll get back just the monthlies + quarterlies in the next 90 days,
sorted by DTE.

## Same enrichment in `/v2/options/expiry-summary`

If you already use [`/v2/options/expiry-summary`](/api/v2/options/expiry-summary),
each row is enriched with the same `type`, `is_anchor`, `expiry_date`,
`notional_oi_usd`, and `max_pain` fields. Plus top-level `anchor_count`
and `type_counts` so you can render summary stats without iterating.

## How to use this in production

**Pre-OPEX setup (T-5 to T-1)**: filter to next anchor, watch the
gamma walls move as positions unwind/roll. Big call\_resistance moves
upward = bullish positioning rolling forward.

**OPEX day**: the `max_pain` strike on the anchor expiry is a magnet.
Combined with [GEX levels](/concepts/gex), you get a tight pin
prediction window for the close.

**Post-OPEX**: the next anchor's expected\_move and OI tell you whether
positioning has compressed (low IV, low OI = sell-vol environment) or
expanded (high IV, high OI = vol expansion likely).

## Related concepts

<CardGroup cols={2}>
  <Card title="Max pain" icon="bullseye" href="/concepts/max-pain">
    The pinning strike on each expiry — a key OPEX-day signal.
  </Card>

  <Card title="What is GEX?" icon="chart-line" href="/concepts/gex">
    The walls / HVL / support levels OPEX positioning concentrates in.
  </Card>

  <Card title="The IV suite" icon="wave-square" href="/concepts/iv-suite">
    Term structure flattening / steepening around OPEX is a big signal.
  </Card>
</CardGroup>