> For the complete documentation index, see [llms.txt](https://docs.strikelabs.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.strikelabs.app/api-reference/series-ids.md).

# Series IDs

Every option contract has one canonical name:

```
{SYMBOL}-{EXPIRY_TS}-{RIGHT}-{STRIKE}
```

```
NVDA-1786492800-C-221
│    │          │ │
│    │          │ └── strike, 221
│    │          └──── right: C call, P put
│    └───────────────  expiry, unix seconds (UTC)
└────────────────────  underlying
```

A `seriesId` is what you pass to [`/v1/order`](/api-reference/exchange.md#place-an-order) and [`/v1/book`](/api-reference/info.md#book), and what comes back on fills, positions and prints. It is stable for the life of the contract.

## Strikes

The strike is written without trailing zeros: `221`, not `221.0`. Half strikes appear as `222.5`. Strike spacing varies by underlying price — dollar increments on cheaper names, wider on expensive ones.

## sid

Alongside `seriesId`, listing responses carry a `sid`: a small integer alias.

```json
{ "seriesId": "NVDA-1786492800-C-221", "sid": 259 }
```

`sid` exists for the maker's binary wire, where four bytes beat a twenty-character string across tens of thousands of rows per second. It is assigned when a series is listed and is **stable only for the lifetime of a venue process** — a restart may renumber. Never persist a `sid`; persist the `seriesId` and re-resolve.

## Discovering series

[`/v1/series?symbol=NVDA`](/api-reference/info.md#series) returns every live series for a symbol. Settled and expired contracts are filtered out, so what you get back is what you can trade.

Expect a large response: a symbol with daily, weekly and monthly expiries across a full strike ladder carries well over a thousand series. Group by `expiryTs` to build an expiry picker, then call [`/v1/chain`](/api-reference/info.md#chain) for the one expiry you want to display.


---

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