Open Interest Simulator API

Endpoint

Parameters

Request

curl -H "X-Api-Key: YOUR_API_KEY" \
  "https://lab.flashalpha.com/v1/flow/oi/SPY"

import requests

resp = requests.get(
    "https://lab.flashalpha.com/v1/flow/oi/SPY",
    headers={"X-Api-Key": "YOUR_API_KEY"}
)
resp.raise_for_status()
data = resp.json()
print(f"Official OI:  {data['official_oi']:,}")
print(f"Effective OI: {data['effective_oi']:,}")
print(f"Intraday delta: {data['intraday_oi_delta']:,}")

const resp = await fetch(
  "https://lab.flashalpha.com/v1/flow/oi/SPY",
  { headers: { "X-Api-Key": "YOUR_API_KEY" } }
);
if (!resp.ok) throw new Error(`HTTP ${resp.status}`);
const data = await resp.json();
console.log(`Official OI:  ${data.official_oi.toLocaleString()}`);
console.log(`Effective OI: ${data.effective_oi.toLocaleString()}`);
console.log(`Intraday delta: ${data.intraday_oi_delta.toLocaleString()}`);

{
  "symbol": "SPY",
  "as_of": "2026-10-30T13:45:49.7452098Z",
  "expiry": null,
  "official_oi": 18161399,
  "simulated_oi": 18186080,
  "intraday_oi_delta": 24681,
  "oi_delta_confidence": 0.43,
  "effective_oi": 18187654,
  "contracts_total": 12318,
  "contracts_with_flow": 1382,
  "endpoint_version": "2026.09.30",
  "data_as_of": {
    "node": "fa5",
    "equity_feed": "2026-10-30T13:45:49.435Z",
    "equity_options_feed": "2026-10-30T13:45:48Z",
    "index_feed": "2026-10-30T13:45:47.104Z",
    "index_options_feed": "2026-10-30T13:45:45Z",
    "futures_feed": "2026-10-30T13:45:48.621Z",
    "futures_options_feed": "2026-10-30T13:45:49.081Z",
    "flow_feed": "2026-10-30T13:45:00Z",
    "oi_feed": "2026-10-29T20:00:00Z",
    "macro_feed": "2026-10-29T21:00:20Z"
  }
}

Response Fields

effective_oi can differ from max(0, simulated_oi) because the clamp is applied per-contract before aggregation.

Errors

About Flow OI

Flow OI exposes the raw simulator state that powers the rest of the /v1/flow/* family. official_oi matches the morning OPRA-broadcast OI used by the settled /v1/exposure/* endpoints. effective_oi is the per-contract clamped quantity the live analytics consume, and simulated_oi is the unclamped aggregate, which can deviate when sell pressure overshoots a contract's OI to zero. The intraday_oi_delta is the true signed sum from the simulator and intentionally cannot be reconstructed from (effective - official) - use this field if you're building your own analytics on top of the simulator.

Common Use Cases

• Build custom analytics - drive your own GEX/DEX or pin-risk variants off effective_oi, the same per-contract clamped quantity the live Flow endpoints consume
• Audit and reconcile - surface the gap between official_oi, simulated_oi, and effective_oi to catch overshoot or clamping artefacts before they reach exposure numbers
• Read directional flow - the sign of intraday_oi_delta shows whether the day is net opening or net closing interest, the input to opening-vs-closing bias
• Weight by confidence - scale signal size by oi_delta_confidence and de-rate the read when the simulator is less certain about the intraday delta
• Gauge session breadth - contracts_with_flow / contracts_total is a rough activity-heat measure for how much of the chain is repositioning
• Power research workflows - pair with historical exposure snapshots to study how intraday OI flow predicts end-of-day positioning

Related

Related reading

• Opening vs closing bias: the options flow OI simulator - how signed intraday OI deltas distinguish opening from closing interest
• Effective open interest: live GEX from flow - the methodology that turns effective OI into live exposure

Complementary endpoints

• OI Diff - day-over-day open-interest changes by strike
• Flow Live Bundle - the raw real-time tape feeding the simulator
• Flow GEX - live flow-adjusted gamma built on this effective OI