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

# Messages

> Reference the Messages-compatible request, response, thinking, tools, structured output, and SSE behavior.

```text theme={null}
POST /inf/v1/messages
```

The route always returns Messages-shaped output and errors, independent of the selected provider family.

## Request

```bash theme={null}
curl https://llm.example.com/inf/v1/messages \
  -H "Authorization: Bearer $AIRMUX_INFERENCE_KEY" \
  -H 'Content-Type: application/json' \
  -d '{
    "model": "anthropic/claude-sonnet-4-6",
    "max_tokens": 128,
    "system": "Be concise.",
    "messages": [{"role": "user", "content": "Say hello"}]
  }'
```

## Fields

| Field                  | Notes                                                      |
| ---------------------- | ---------------------------------------------------------- |
| `model`                | Required catalog model ID                                  |
| `messages`             | User and assistant Messages content                        |
| `system`               | String or supported text-block array                       |
| `max_tokens`           | Required; minimum 1; maps to canonical `max_output_tokens` |
| `stream`               | Boolean                                                    |
| `temperature`, `top_p` | Sampling fields                                            |
| `stop_sequences`       | Maps to the gateway's internal stop sequences              |
| `tools`, `tool_choice` | Tool definitions and selection                             |
| `thinking`             | Reasoning type, token budget, and display settings         |
| `output_config`        | Reasoning effort and structured-output format              |

Other top-level fields, such as `top_k`, `metadata`, and `service_tier`, travel as provider extras when the selected profile accepts them.

## Response

```json theme={null}
{
  "id": "019...",
  "type": "message",
  "role": "assistant",
  "model": "anthropic/claude-sonnet-4-6",
  "content": [{"type": "text", "text": "Hello!"}],
  "stop_reason": "end_turn",
  "usage": {"input_tokens": 8, "output_tokens": 2},
  "gateway": {"finish_reason": "stop", "adjustments": []}
}
```

Reasoning signatures are opaque provider values. Replay the complete thinking block unchanged on a later turn when the SDK includes it.

## Streaming

The response uses named Messages events: `message_start`, `ping`, content block start/delta/stop events,
`message_delta`, and `message_stop`. The terminal `message_delta` carries final usage and the additive `gateway` object.

See [Use an SDK](/docs/guides/sdks) for an Anthropic client example.