Anthropic Messages and Claude Code

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.

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.

With Anthropic’s SDKs

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)

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.

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:

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.

Counting 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. They carry no code: use the HTTP status and error.type.

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