Install & Authenticate

One npm install, three auth paths

Claude Code is a single npm package — @anthropic-ai/claude-code. Once installed it's claude on your PATH. The interesting choice is authentication, because it determines how you're billed and how your sessions get tracked.

OAuth via Claude Max / Pro. Run claude, follow the browser flow, done. Token lives in ~/.claude.json. Best for individuals — your usage rolls up under the same subscription as Claude.ai. No API key to rotate, no env var to forget.

API key. Set ANTHROPIC_API_KEY in the environment. Pay-as-you-go billing, programmatic key rotation, what every CI server uses. Treat the key like a deploy credential — never commit, always inject.

Cloud provider routing. CLAUDE_CODE_USE_BEDROCK=1 or CLAUDE_CODE_USE_VERTEX=1 route through AWS Bedrock or Google Vertex AI. Enterprises use this when their data-residency or procurement story requires the model to live behind their cloud account.

After install, claude doctor is your first stop for any "it doesn't work" question — it checks node version, PATH, auth, and connectivity in one command.

Code

Install on a fresh machine·bash

# Prereqs
node --version    # 18+
npm --version

# Install globally
npm install -g @anthropic-ai/claude-code

# First run — triggers OAuth in browser if no API key set
cd ~/myproject
claude

# Health check
claude doctor

API key path (CI / servers / fleet)·bash

# Persistent in shell
echo 'export ANTHROPIC_API_KEY="sk-ant-..."' >> ~/.zshrc
source ~/.zshrc

# Or via direnv per-project (.envrc, gitignored)
echo 'export ANTHROPIC_API_KEY="sk-ant-..."' >> .envrc
direnv allow

# CI: never echo the key, never log it
# GitHub Actions: ${{ secrets.ANTHROPIC_API_KEY }}

One npm install, three auth paths

Code

External links

Exercise

Progress

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