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·4 min readenv-varstutorialclaude

The ANTHROPIC_BASE_URL Trick: One Env Var, 80% Off Every Anthropic Tool

ANTHROPIC_BASE_URL is the most underrated env var in AI tooling. Set it once and every Anthropic-compatible tool — Claude Code, Cline, OpenClaw, Aider, Continue — runs through your custom endpoint at 80% off.

The most underrated env var in AI tooling

If you've used Claude Code, you might know ANTHROPIC_BASE_URL. If you've used Cline, OpenClaw, Aider, OpenCode, Goose, or any other tool built on the Anthropic Python or Node SDK — you can use it there too. The same single environment variable redirects every Anthropic-compatible tool on your machine to a custom endpoint.

Set it once at the shell level, and every Claude tool you launch from that shell routes through your override.

What it does

ANTHROPIC_BASE_URL overrides the default https://api.anthropic.com that the Anthropic SDK uses. The SDK reads it on initialization. So does every tool that uses the SDK.

The same trick exists for OpenAI: OPENAI_BASE_URL. And for Google AI Studio (less consistent across tools): GOOGLE_BASE_URL or per-tool config.

Set it once, save everywhere

In your shell profile (~/.zshrc, ~/.bashrc, ~/.config/fish/config.fish):

export ANTHROPIC_BASE_URL="https://claudeapi.cheap/api/proxy"
export ANTHROPIC_API_KEY="sk-cc-your-key-here"
# Or for tools that use AUTH_TOKEN instead of API_KEY:
export ANTHROPIC_AUTH_TOKEN="sk-cc-your-key-here"

Reload your shell (source ~/.zshrc or open a new terminal). From now on, every Anthropic-SDK-based tool launched from that shell uses the override.

What this affects

A non-exhaustive list of tools that pick up ANTHROPIC_BASE_URL:

  • Claude Code — Anthropic's official terminal agent.
  • Cline (with explicit setting in Cline's UI, or env-driven for the underlying SDK).
  • OpenClaw — autonomous agent.
  • Aider — pair programming CLI.
  • OpenCode — open-source Claude Code alternative.
  • OpenHands (formerly OpenDevin) — autonomous SWE agent.
  • Goose — Block's AI agent.
  • Continue.dev — VS Code/JetBrains assistant (via apiBase in config).
  • Cursor — when you tick "Override Anthropic Base URL" in settings.
  • Direct SDK code — anything you write with anthropic (Python) or @anthropic-ai/sdk (Node).
  • LangChain, LlamaIndex — when you don't pass an explicit base_url argument.
  • Any HTTP wrapper that doesn't hardcode the URL.

    • It does NOT affect:

  • Web-based Claude (claude.ai) — that's Anthropic's UI on Anthropic's servers, not an API call.
  • Cursor Tab — uses Cursor's hosted model, not your API key.
  • Any tool with a hardcoded URL. Some niche tools build the URL into their binary. These can't be redirected without recompiling.

    • Why this works (for the curious)

    The Anthropic SDK's source code has a check like process.env.ANTHROPIC_BASE_URL ?? "https://api.anthropic.com" at construction time. The SDK then hits whatever URL is configured. As long as the URL responds with the same JSON shape Anthropic returns, every downstream call works.

    claudeapi.cheap is a strict superset of the Anthropic API — same routes, same auth, same request shape, same response shape, same SSE event types for streaming. We strip vendor-fingerprint headers (so the upstream identity stays hidden) but never modify content.

    Same trick for OpenAI and Gemini

    export OPENAI_API_KEY="sk-cc-your-key-here"
export OPENAI_BASE_URL="https://claudeapi.cheap/api/proxy/v1"

    The same sk-cc-... key works for both providers. Our /v1/chat/completions route also serves Gemini models — pick gemini-3-pro-preview or gemini-2.5-flash as the model id.

    Result: one environment, three vendors, every tool 80% off.

    Project-scoped overrides

    Don't want this active everywhere? Use direnv to scope env vars to specific directories:

    # In your project's .envrc:
export ANTHROPIC_BASE_URL="https://claudeapi.cheap/api/proxy"
export ANTHROPIC_API_KEY="sk-cc-your-key-here"

    Then direnv allow once. Every shell entering that directory inherits the override; every shell elsewhere uses Anthropic Direct.

    Verifying the override works

    Quick test from any shell:

    echo $ANTHROPIC_BASE_URL
# → https://claudeapi.cheap/api/proxy

curl -s $ANTHROPIC_BASE_URL/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"claude-haiku-4-5","max_tokens":10,"messages":[{"role":"user","content":"hi"}]}'
# → JSON response with id starting chatcmpl- or msg_

    If the JSON comes back, your env is set correctly and every tool that respects the env will inherit.

    Get started

    Sign up free, grab an sk-cc-... key, paste two export lines into your shell profile. Every Anthropic tool on your machine is now 80% cheaper without changing a single line of tool code.