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

# Regional Execution

> Models run where the data lives. Requests route to the lowest-latency region by default; pin a region or geographic zone with the X-Region-Override and X-World-Part-Override headers.

Models run where the data lives.

By default, each request routes to the closest available region. Two HTTP headers override that: `X-Region-Override` pins a specific region, and `X-World-Part-Override` keeps traffic within a broader geographic zone.

|                     | `X-World-Part-Override`                                         |
| ------------------- | --------------------------------------------------------------- |
| **Scope**           | Geographic zone                                                 |
| **Example value**   | `eu`                                                            |
| **Use when**        | You want to stay in a geography without picking an exact region |
| **If both are set** | Ignored                                                         |

## Default behavior

When you make a request without any region headers, it routes to the closest available region. No configuration needed.

## World-part constraints

Keep traffic within a geographic zone with `X-World-Part-Override`. The best available region within that zone is selected. Use this when you need to stay within a geography but do not need a specific data center.

```bash theme={null}
curl https://api.slng.ai/v1/tts/slng/deepgram/aura:2-en \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -H "X-World-Part-Override: eu" \
  -d '{ "voice": "aura-2-thalia-en", "text": "Hello from somewhere in Europe!" }' \
  --output hello.wav
```

## World parts

A world part groups several regions under one value. Requests route to the best available region within that zone, which does not guarantee a specific country.

| Value       | Zone           |
| ----------- | -------------- |
| `na`        | North America  |
| `eu`        | Europe         |
| `eu-non-eu` | Europe, non-EU |
| `ap`        | Asia-Pacific   |
| `me`        | Middle East    |

<Warning>
  If your compliance requirement depends on a specific country, use `X-Region-Override` with the exact region. A world part routes to the best region within a zone and does not guarantee a specific country.
</Warning>

## Compliance

Regional execution is not just about latency. In regulated industries it determines where data can exist and which models can process it. These constraints are respected per request.

If you need a particular model hosted in a region where it is not currently available, [contact us](mailto:support@slng.ai).

## Next steps

<CardGroup cols={2}>
  <Card title="Models by region" icon="globe" href="/models/by-region">
    See which models are deployed in each region.
  </Card>

  <Card title="Context Router" icon="shuffle" href="/context-router">
    How geography is one of four dimensions the layer adapts on.
  </Card>
</CardGroup>