> ## 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-Region-Override`             | `X-World-Part-Override`                                         |
| ------------------- | ------------------------------- | --------------------------------------------------------------- |
| **Scope**           | Exact region                    | Geographic zone                                                 |
| **Example value**   | `eu-north-1`                    | `eu`                                                            |
| **Use when**        | You need a specific data center | You want to stay in a geography without picking an exact region |
| **If both are set** | Wins                            | Ignored                                                         |

## Default behavior

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

## Region pinning

Pin to a specific data center with `X-Region-Override`. Use this when you have data-residency or compliance requirements that depend on a specific location.

```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-Region-Override: eu-north-1" \
  -d '{ "voice": "aura-2-thalia-en", "text": "Hello from Europe!" }' \
  --output hello.wav
```

## 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
```

If both headers are present, `X-Region-Override` wins.

## Available regions

Not every model is deployed in every region. Check [Models by Region](/models/by-region) to see what is available where.

| World part | Region ID              | Location     |
| ---------- | ---------------------- | ------------ |
| `na`       | `us-east-1`            | US East      |
| `eu`       | `eu-north-1`           | EU North     |
| `ap`       | `ap-south-1`           | AP South     |
| `ap`       | `ap-southeast-2`       | AP Southeast |
| `ap`       | `asia-south1`          | AP South     |
| `ap`       | `asia-southeast2`      | Jakarta      |
| `ap`       | `australia-southeast1` | Sydney       |

## 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>

## Voice agent region config

Voice agents use a separate `region` field (`us-east`, `eu-central`, `ap-south`) that determines where the agent runs. It is not interchangeable with the platform headers above: the agent region `ap-south`, for example, routes to the platform region `ap-south-1`, but you set it through a different field. See the [Voice Agents region table](/voice-agents#agent-regions) for the full mapping and the telephony country pinning each region applies.

## 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="Adaptive Execution" icon="shuffle" href="/execution-layer/adaptive">
    How geography is one of four dimensions the layer adapts on.
  </Card>
</CardGroup>