# Open interest by position size | API reference | Femtos

> Long and short open interest of a perp by position size, every hour since September 2025. GET /v1/hypercore/oi/cohorts on HyperCore: parameters, response fields and a live call per layer.

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- Decimals are exact strings, times Unix milliseconds, addresses lowercase `0x`
- Whole API in one file: https://femtos.xyz/agents.md · OpenAPI: https://api.femtos.xyz/v1/openapi.json · Index: https://femtos.xyz/llms.txt
- Page with live calls: https://femtos.xyz/reference/open-interest-cohorts

## Open interest by position size — GET `/v1/hypercore/oi/cohorts`

Long and short open interest of a perp by position size, every hour since September 2025.

Layers: HyperCore. Not on Elysium or HyperEVM: the EVM layers trade on AMM pools, with no order book: pool detail and liquidity events cover a pool.
Page with live calls: https://femtos.xyz/reference/open-interest-cohorts?layer=hypercore

| Param | In | Example or values | Meaning |
|---|---|---|---|
| `coin` | query | `BTC` | Perp market: BTC, xyz:TSLA |
| `every` | query | `(empty)`, `1h`, `1d` | 1h: every hourly funding; 1d: the first of each day |
| `from` | query | (optional) | Start (ms, inclusive). Without it: the `limit` points ending at `to` |
| `to` | query | (optional) | End (ms, exclusive; default now) |
| `limit` | query | `24` | Points (744: a month of hours) |

```bash
curl -H "Authorization: Bearer $FEMTOS_KEY" "https://api.femtos.xyz/v1/hypercore/oi/cohorts?coin=BTC&every=1h&limit=24"
```

| Field | Type | Meaning |
|---|---|---|
| `points[]` | object | Ascending: {t, block, px, oi, longAccounts, shortAccounts, top10Long, top10Short, cohorts} |
| `points[].cohorts[]` | object | One per tier with positions, smallest first: {tier, longSz, shortSz, longAccounts, shortAccounts} |
| `points[].top10Long` | decimal | Size of the 10 largest longs together |
| `points[].oi` | decimal | Open interest (size) |
| `tiers[]` | object | The size tiers: {tier, minUsd, maxUsd} |

## Related (Liquidations & positions)

- [Liquidations](https://femtos.xyz/reference/liquidations.md) `GET /v1/liquidations`: Perp liquidations, newest first, one row per account, coin and block. (HyperCore)
- [Liquidations stream](https://femtos.xyz/reference/ws/liquidations.md) `WS hc.liquidations`: Each liquidation fill, the block it happens. One frame per block with all its matching events. (HyperCore)
- [Liquidation stats](https://femtos.xyz/reference/liquidation-stats.md) `GET /v1/liquidations/stats`: Totals, per coin, per time bucket and the largest, over a window. (HyperCore)
- [Liquidation stats stream](https://femtos.xyz/reference/ws/liquidation-stats.md) `WS hc.liquidations.stats`: The GET /v1/liquidations/stats answer (totals, per coin, per bucket, the largest), pushed on subscribe, then when a liquidation comes in (whole, or as a JSON Patch). (HyperCore)
- [Positions](https://femtos.xyz/reference/positions.md) `GET /v1/positions`: Open positions of one perp with leverage and liquidation price. (HyperCore)
- [Position changes](https://femtos.xyz/reference/ws/positions.md) `WS hc.positions`: Each perp position change, one per block, account and coin. One frame per block with all its matching events. (HyperCore)
- [Open positions stream](https://femtos.xyz/reference/ws/positions-open.md) `WS hc.positions.open`: The GET /v1/positions answer of one perp (size, entry, PnL, leverage, liquidation price), pushed on subscribe, then on each roll of the live positions (every 5 s) when it changes. (HyperCore)
- [Position change history](https://femtos.xyz/reference/position-changes.md) `GET /v1/positions/changes`: Past perp position changes of one coin over a size, one row per account and block. (HyperCore)
- [Open interest](https://femtos.xyz/reference/positions-overview.md) `GET /v1/positions/overview`: Open interest, accounts and unrealized PnL per perp. (HyperCore)
- [Open interest stream](https://femtos.xyz/reference/ws/positions-overview.md) `WS hc.positions.overview`: The GET /v1/positions/overview answer (long / short open interest, accounts, unrealized PnL per perp), pushed on subscribe, then on each roll of the live positions (every 5 s) when it changes (whole, or as a JSON Patch). (HyperCore)
- [Liquidation map](https://femtos.xyz/reference/liqmap.md) `GET /v1/positions/liqmap`: Notional that would be liquidated at each price around the mark. (HyperCore)
- [Liquidation levels stream](https://femtos.xyz/reference/ws/positions-liqmap.md) `WS hc.positions.liqmap`: The GET /v1/positions/liqmap answer of one perp (notional liquidated per price bucket), pushed on subscribe, then on each roll of the live positions (every 5 s) when it changes. (HyperCore)
- [Open interest history](https://femtos.xyz/reference/open-interest.md) `GET /v1/hypercore/oi`: Open interest bars of a perp since May 2023, after every block since March 2025: longs and shorts opened, closed, liquidated. (HyperCore)
- [Open interest per block](https://femtos.xyz/reference/ws/oi.md) `WS hc.oi`: The open interest of a perp after every block with a fill: longs and shorts opened, closed, liquidated. One frame per block with all its matching events. (HyperCore)
- [Open interest by market](https://femtos.xyz/reference/open-interest-markets.md) `GET /v1/hypercore/oi/markets`: Every perp's open interest now, its 1 h / 24 h / 7 d change, totals per dex. (HyperCore)
- [Who opened positions](https://femtos.xyz/reference/open-interest-opens.md) `GET /v1/hypercore/oi/opens`: The largest orders that opened longs or shorts on a perp in a window, with the account and whether it crossed the spread. (HyperCore)

Every page: https://femtos.xyz/reference.md