Claude Code with API429: installation, API key and model setup

Choose a small first task

Start with a short, nonconfidential text question in a disposable project. This keeps the first check focused on the endpoint, authentication and exact model ID before you send source files or approve commands. Claude Code is a terminal application; its local permissions and available features depend on the installed client version. An API429 key establishes model access only where the client and request contract support the same operation.

The public API429 reference describes POST /v1/messages, x-api-key authentication and Anthropic SSE events. Those facts support the connection settings below. They do not establish that every Claude Code beta field, streaming behavior or tool loop works through this connection. Native CLI execution was not performed for this guide, and a successful basic text response would still require separate agent testing.

Install for your operating system

Use the official native installer for macOS, Linux or WSL, and the separate official PowerShell installer on Windows. Review the manufacturer installation instructions before running an installer. Open a fresh terminal after installation and check claude --version. The reviewed manufacturer guidance requires Claude Code 2.1.284 or later for Claude Sonnet 5.5. Native installation does not require a prior Node.js installation.

Windows can use PowerShell or CMD without mandatory WSL. Git for Windows is optional; without it, shell commands use PowerShell. Choose WSL 2 when your project needs Linux tools or a supported sandbox, and install the client inside that distribution. The reviewed setup requirements include internet access and at least 4 GB of RAM. Keep the initial test outside a repository containing credentials.

Set the origin, key and model explicitly

Set ANTHROPIC_BASE_URL to https://gateway.api429.com without /v1. Claude Code appends /v1/messages, so a base URL ending in /v1 can produce an incorrect repeated path. Use ANTHROPIC_API_KEY for the API429 client key: this variable supplies x-api-key. ANTHROPIC_AUTH_TOKEN uses Bearer authentication instead; copying an OpenAI authorization example into this configuration changes the authentication contract.

Set the model to claude-sonnet-5-5 and preserve every hyphen. Check GET /v1/models using your own key before selecting it: a public model card does not prove availability under a particular credential. The examples read the key with hidden terminal input and keep it in the current session. Never pass the real key as a command argument, commit it to project settings or paste it into diagnostic messages.

Inspect the session before sending project content

Launch claude from the terminal where you set the environment variables. Use /status to inspect the base URL and authentication source without publishing the credential value. If a saved account, unexpected source or different model appears, resolve that configuration conflict before submitting private code. A saved setting alone does not prove a completed request.

After a bounded text check, decide whether you need persistent user configuration. User-level ~/.claude/settings.json is separate from a shared project .claude/settings.json. Keep secrets out of project files and version control. The PowerShell and Bash examples launch the client; a subsequent model request may consume paid API usage. Review proposed file changes and commands before allowing an agent task.

Diagnose errors and separate the bills

For a 401 response, check the key and x-api-key authentication source. For 404, inspect the base URL and final request path. A model error calls for an exact comparison with the list returned for your key. When text works but a tool or stream fails, retain only a redacted error and inspect the specific request feature before trying a larger task.

There is no fixed hourly cost for coding. Context size, response length, repeated requests and agent actions change token usage. Check current API429 rates and actual usage in your account. Claude Code application access, subscription features and API charges are separate matters; this connection does not promise all subscription capabilities. A catalog entry or documented SSE format cannot substitute for testing the installed client.

Install on macOS, Linux or WSL

curl -fsSL https://claude.ai/install.sh | bash
claude --version

Install with Windows PowerShell

irm https://claude.ai/install.ps1 | iex
claude --version

Session configuration with hidden key entry

export ANTHROPIC_BASE_URL="https://gateway.api429.com"
read -rs -p "API429 key: " ANTHROPIC_API_KEY; printf "\n"
export ANTHROPIC_API_KEY
export ANTHROPIC_MODEL="claude-sonnet-5-5"
claude --model claude-sonnet-5-5

PowerShell session configuration with protected key entry

$env:ANTHROPIC_BASE_URL = "https://gateway.api429.com"
$env:ANTHROPIC_API_KEY = [System.Net.NetworkCredential]::new("", (Read-Host "API429 key" -AsSecureString)).Password
$env:ANTHROPIC_MODEL = "claude-sonnet-5-5"
claude --model claude-sonnet-5-5

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