# Anthropic Messages and Claude Code

> POST /v1/messages for Claude models with the Anthropic SDKs, Claude Code and anything else that speaks Anthropic's API.

Source: https://zurelay.com/docs/anthropic

Claude models also speak Anthropic’s Messages API, so Anthropic’s SDKs, Claude Code and anything built for them work with a new base URL and key.

`POST /v1/messages`

Base URL `https://api.zurelay.com` (the SDKs add `/v1/messages`). Send the key as `x-api-key` or `Authorization: Bearer`, with `anthropic-version: 2023-06-01`. Only Claude models are served here; other models use [/v1/chat/completions](https://zurelay.com/docs/chat).

## With Anthropic’s SDKs

**Python** (`main.py`):

```python
import os
import anthropic

client = anthropic.Anthropic(
    base_url="https://api.zurelay.com",
    api_key=os.environ["ZURELAY_API_KEY"],
)

message = client.messages.create(
    model="claude-opus-5-5",
    max_tokens=1024,
    system="You are a careful code reviewer.",
    messages=[{"role": "user", "content": "Review this function: def add(a, b): return a - b"}],
)
print(message.content[0].text)
```

**Node.js** (`index.mjs`):

```javascript
import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  baseURL: "https://api.zurelay.com",
  apiKey: process.env.ZURELAY_API_KEY,
});

const message = await client.messages.create({
  model: "claude-opus-5-5",
  max_tokens: 1024,
  system: "You are a careful code reviewer.",
  messages: [{ role: "user", content: "Review this function: def add(a, b): return a - b" }],
});
console.log(message.content[0].text);
```

**cURL**:

```bash
curl https://api.zurelay.com/v1/messages \
  -H "x-api-key: $ZURELAY_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-opus-5-5",
    "max_tokens": 1024,
    "messages": [{ "role": "user", "content": "Hello, Claude" }]
  }'
```

Everything in Anthropic’s Messages API passes through (except `metadata`, which stays with us): `system` as a string or blocks (with `cache_control` for prompt caching), `tools`, `thinking`, `stop_sequences`, `temperature`, streaming with the same events, and `anthropic-beta` headers. Images and PDFs go in as `image` and `document` blocks: see [Images, PDFs, audio and video](https://zurelay.com/docs/multimodal).

## Claude Code

Point Claude Code at zurelay with five environment variables (the base URL, your key and the three model aliases), then run it as usual:

Shell:

```bash
export ANTHROPIC_BASE_URL="https://api.zurelay.com"
export ANTHROPIC_AUTH_TOKEN="$ZURELAY_API_KEY"
export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-5-5"
export ANTHROPIC_DEFAULT_SONNET_MODEL="claude-sonnet-5-5"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="claude-sonnet-5-5"

claude
```

To keep it, put the same values in the `env` block of `~/.claude/settings.json`. The full guide, and guides for Cursor, Cline and others, are under [Integrations](https://zurelay.com/docs/integrations).

## Counting tokens

`POST /v1/messages/count_tokens`

Takes the same body as `/v1/messages` and returns `{ "input_tokens": 1234 }`, an estimate of what the request would count. Free.

## Errors

Errors come back in Anthropic’s shape (`{ "type": "error", "error": { "type", "message" } }`), with the same meanings as on the [errors page](https://zurelay.com/docs/errors). They carry no `code`: use the HTTP status and `error.type`.

> **Note:** A few Claude models read PDFs only through `/v1/chat/completions`. Send one to `/v1/messages` and the error says which endpoint to use. The table on [Images, PDFs, audio and video](https://zurelay.com/docs/multimodal) shows what each model reads.

- **Tip:** Anthropic’s token counter and ours can differ slightly; usage in the response is what’s billed.