anthropic-proxy

Reverse proxy that lets OpenCode (and similar tools) use a Claude subscription instead of an API key.

Prerequisites

• Go 1.26+

Optional: Nix flake for dev shell (nix develop).

Setup

cp config.example.yaml config.yaml

Edit config.yaml:

• api_keys — key(s) your clients use to authenticate with the proxy
• claude_binary — optional path to claude binary (used for request fingerprinting via sniff only)

Authentication

On first run, if no credentials are found at ~/.claude/.credentials.json, the proxy starts an OAuth login flow in your browser. Credentials are stored at ~/.claude/.credentials.json (the same file Claude Code CLI uses). On subsequent runs, existing credentials are reused and refreshed automatically.

If running headlessly (SSH/server), the authorization URL is printed to stdout and you can paste the authorization code manually.

If you've already logged in with Claude Code CLI, the proxy will use the same credentials.

Build and run

go build -o anthropic-proxy .
./anthropic-proxy

Usage with OpenCode

export ANTHROPIC_API_KEY=your-proxy-api-key
export ANTHROPIC_BASE_URL=http://localhost:8082
opencode

Endpoints

Method	Path	Description
POST	/v1/messages	Anthropic messages API (proxied)
POST	/messages	Same, without /v1 prefix
GET	/healthz	Health check
POST	/reload	Hot-reload config.yaml

Request sanitization

The sanitize section in config renames tool names and replaces strings in system prompts before forwarding to Anthropic. Responses are de-sanitized before returning to the client.

See config.example.yaml for the default rules.

Reload after editing config:

curl -X POST localhost:8082/reload