Options Block Trades API - Large Print Detection

Endpoint

GET /v1/flow/options/{symbol}/blocks

Auth required (X-Api-Key) Rate Limited: Yes Alpha plan+

Parameters

Name	In	Required	Default	Description
`symbol`	path	yes	-	Underlying symbol
`minSize`	query	no	100	Minimum contract size

curl -H "X-Api-Key: YOUR_API_KEY" \
  "https://lab.flashalpha.com/v1/flow/options/SPY/blocks?minSize=250"

import requests

resp = requests.get(
    "https://lab.flashalpha.com/v1/flow/options/SPY/blocks",
    headers={"X-Api-Key": "YOUR_API_KEY"}
)
data = resp.json()
print(f"{data['count']} blocks at minSize {data['minSize']}")

const resp = await fetch(
  "https://lab.flashalpha.com/v1/flow/options/SPY/blocks",
  { headers: { "X-Api-Key": "YOUR_API_KEY" } }
);
const data = await resp.json();
console.log(data.count + " blocks at minSize " + data.minSize);

API Key

Response

{
  "symbol": "SPY",
  "minSize": 250,
  "count": 2,
  "blocks": [
    {
      "ts": "2026-05-12T18:41:55.108Z",
      "expiry": "2026-05-15",
      "strike": 600.0,
      "right": "C",
      "price": 1.85,
      "size": 1500,
      "side": "buy"
    },
    {
      "ts": "2026-05-12T18:38:12.402Z",
      "expiry": "2026-06-20",
      "strike": 590.0,
      "right": "P",
      "price": 4.30,
      "size": 800,
      "side": "sell"
    }
  ]
}

Key Response Fields

Field	Type	Description
`symbol`	string	Uppercase underlying symbol
`minSize`	integer	Minimum block size applied
`count`	integer	Number of block trades returned
`blocks[]`	array	Block rows: `ts`, `expiry`, `strike`, `right`, `price`, `size`, `side`

Errors

Status	Description
`403`	Requires Alpha plan or higher
`502`	Upstream flow data source unavailable

About

Filters the option tape to only prints at or above minSize contracts. Default is 100 contracts but you can raise it for institutional-only filtering. Returns rows in the same shape as the recent feed minus instrument id, bid, and ask.

Common Use Cases

Institutional flow tracker: surface 500+ contract prints only
Sweep detection: pair with timestamp clustering for multi-leg sweep identification
Earnings positioning: scan large prints on calendar legs into events
Sentiment overlay: tally buy-side vs sell-side blocks on the day