# Run your first completion

This page sends one chat completion through the gateway, walks through
what came back, and points at the things you'll come back to.

## Send the request

Set your key in an environment variable so it doesn't end up in shell
history:

```bash
export LOWROUTER_API_KEY="lr-sk-..."
```

Then call the gateway:

```bash
curl https://lowrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $LOWROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "lowrouter/auto",
    "messages": [
      {"role": "user", "content": "In one sentence, what is a vector database?"}
    ]
  }'
```

`lowrouter/auto` is the default route. You can pick a specific model
instead — for example `openai/gpt-4o-mini` or
`anthropic/claude-haiku-4-5` — and you can override the route per
request with the `route` field. See [routing](../models/routing).

## What comes back

The response is OpenAI-shaped. The fields you'll use most are:

```json
{
  "id": "chatcmpl-01J9...",
  "object": "chat.completion",
  "created": 1714150000,
  "model": "openai/gpt-4o-mini",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "A vector database stores …"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 18,
    "completion_tokens": 26,
    "total_tokens": 44
  },
  "lowrouter": {
    "generation_id": "gen_01J9...",
    "provider": "openai",
    "region": "eu-west",
    "eco": {
      "energy_wh": 0.0021,
      "carbon_g": 0.00057,
      "carbon_per_1k_tokens_g": 0.013,
      "accuracy": "accurate"
    }
  }
}
```

The OpenAI-compatible parts (`id`, `choices`, `usage`, …) are
documented in [chat completions](../api-reference/chat-completions).
The LowRouter-specific block:

- **`generation_id`** — opaque ID for this request. Pass it to
  [`GET /generation/{id}`](../api-reference/overview) to fetch the full
  record later, or open it on the dashboard with that ID.
- **`provider`** — which upstream actually served the request.
- **`region`** — the region the upstream served from.
- **`eco`** — energy and carbon estimate for this request, with a
  confidence label. Read [methodology](../sustainable-ai/methodology)
  before quoting these numbers anywhere.

## Stream the response

For interactive UIs, set `"stream": true` and read Server-Sent Events:

```bash
curl https://lowrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $LOWROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -N \
  -d '{
    "model": "lowrouter/auto",
    "stream": true,
    "messages": [{"role": "user", "content": "Count to 5 slowly"}]
  }'
```

The stream format and how to consume it from common SDKs is on the
[streaming page](../api-reference/streaming).

## Things that might surprise you

- **The `model` in the response is the resolved model**, not the
  pseudo-model you sent. If you sent `lowrouter/auto`, the response
  tells you what was actually picked.
- **`usage` reflects upstream tokens**, which may include caching
  discounts (for providers that support them). The credits charged on
  your dashboard match this `usage`.
- **The `eco` block is missing on requests we couldn't classify**, e.g.
  a model whose parameter count is unknown. The dashboard shows the
  same record without an eco number rather than a fabricated one.

## Next

[Tour the dashboard →](dashboard-tour)