# Messages (Anthropic format)

> POST /v1/messages in the Anthropic Messages format, used by Claude Code and the Anthropic SDK.

```http
POST https://api.vikey.ai/v1/messages
```

The request and response follow the [Anthropic Messages API](https://docs.anthropic.com/en/api/messages). Claude Code and the Anthropic SDK use this endpoint. Every text model on Vikey can be called through it, including GPT and DeepSeek.

## Example

```bash
curl https://api.vikey.ai/v1/messages \
  -H "x-api-key: YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-5.5",
    "max_tokens": 1024,
    "system": "Answer briefly.",
    "messages": [{"role": "user", "content": "What is the difference between let and const in JavaScript?"}]
  }'
```

`Authorization: Bearer YOUR_API_KEY` is also accepted instead of `x-api-key`.

## Common parameters

| Parameter | Notes |
| --- | --- |
| `model` | Required. A Vikey model id. |
| `max_tokens` | Required in the Anthropic format. Also used for the [balance check](/en/models/pricing/#balance-check). |
| `messages` | Required. `user` and `assistant` messages with text or content blocks (text, images, `tool_use`, `tool_result`). |
| `system` | System prompt, as text or an array of blocks. |
| `stream` | `true` for an Anthropic-format event stream. |
| `tools`, `tool_choice` | Tool use in the Anthropic format. |
| `cache_control` | Cache markers on content blocks are passed to models that support them. |

## Response

```json
{
  "id": "msg_...",
  "type": "message",
  "role": "assistant",
  "model": "anthropic/claude-sonnet-5.5",
  "content": [{"type": "text", "text": "let can be reassigned, const cannot..."}],
  "stop_reason": "end_turn",
  "usage": {"input_tokens": 32, "output_tokens": 58}
}
```

Errors use the Anthropic shape: `{"type": "error", "error": {"type": "...", "message": "..."}}`. See [Errors](/en/api/errors/).

Source: https://docs.vikey.ai/en/api/messages/