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Anthropic base URL for Claude Code: setting ANTHROPIC_BASE_URL correctly

Claude Code talks to whatever address ANTHROPIC_BASE_URL points at. The one rule that trips people up: it wants the bare host, with no /v1 — the opposite of almost every OpenAI-style tool.

The short answer

Set two environment variables before starting Claude Code:

ANTHROPIC_BASE_URL=https://apiclan.us
ANTHROPIC_AUTH_TOKEN=sk-your-key

The official Anthropic address is https://api.anthropic.com; replacing it is all a relay needs. Claude Code appends /v1/messages itself, so the base URL must stop at the host. On this gateway 88% of all Claude traffic in the last 30 days came from Claude Code configured exactly this way.

Where to set it

macOS / Linux — in the shell you launch it from:

export ANTHROPIC_BASE_URL=https://apiclan.us
export ANTHROPIC_AUTH_TOKEN=sk-your-key
claude

Windows PowerShell — for the current window:

$env:ANTHROPIC_BASE_URL = "https://apiclan.us"
$env:ANTHROPIC_AUTH_TOKEN = "sk-your-key"
claude

~/.claude/settings.json — so every session picks it up without touching the shell:

{
  "env": {
    "ANTHROPIC_BASE_URL": "https://apiclan.us",
    "ANTHROPIC_AUTH_TOKEN": "sk-your-key"
  }
}

The value is read when Claude Code starts. If you change it, quit and start a new session; an open one keeps the old address. ANTHROPIC_AUTH_TOKEN is sent as Authorization: Bearer; ANTHROPIC_API_KEY is sent as x-api-key. This gateway accepts either, so use one, not both.

Test it in one command

Before blaming Claude Code, check the address and key directly:

curl https://apiclan.us/v1/messages \
  -H "Authorization: Bearer sk-your-key" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"claude-sonnet-5","max_tokens":20,"messages":[{"role":"user","content":"hi"}]}'

A JSON reply means both are right. text/html or a 404 means the URL is wrong; a 401 in JSON means the URL is right and the key is not.

When to add /v1 and when not to

Two SDK families split the URL at different points. Anthropic-style clients add /v1/messages themselves; OpenAI-style clients expect /v1 in the base URL and add only /chat/completions:

Client	Base URL
Claude Code, Anthropic SDK	https://apiclan.us
Codex, OpenAI SDK	https://apiclan.us/v1
Cursor, Cline, Roo Code	https://apiclan.us/v1
Cherry Studio, Chatbox, LobeChat, LM Studio	https://apiclan.us/v1

Put /v1 in Claude Code and requests go to /v1/v1/messages, which returns a 404. Leave it out of Cursor and they go to /chat/completions — also a 404. Neither reaches the API.

URL mistake or key mistake?

• An error and nothing in your usage log → the path is wrong. A 404 is answered at the edge and never reaches billing. Check /v1 first.
• 401 with a log entry → the key is wrong, revoked, or the balance is empty.
• One model 404s while others work on the same key → that model belongs to a different group. Each key is bound to one group; make a second key for the other group.
• A change seems to have no effect → the variable was set in a different shell, or the session started before you set it.

Choosing the model

Model names are exact strings with hyphens, never dots — claude-fable-5-1, not claude-fable-5.1. Pick one at launch, or with /model inside a session:

claude --model claude-opus-5-5

The current names and prices are on the price list. Setup for other clients is in the quickstart, and the Claude Desktop app is covered in the desktop apps guide.

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