Setting up Claude Opus 4.8 in Claude Code

The claude opus 4.8 claude code setup is straightforward if you already have Node and an API key, but there are sharp edges around model naming and base-URL overrides that waste an hour if missed. This guide walks through a clean install, exact environment configuration, and a verification loop that confirms the agent is actually running Opus 4.8 before you trust it with a refactor.

Step 1: Install Claude Code and confirm the runtime

Claude Code ships as an npm package. You need Node 18+; on older runtimes the binary throws a cryptic ERR_MODULE_NOT_FOUND.

node --version   # expect v18.0.0 or higher
npm install -g @anthropic-ai/claude-code
claude --version

If claude is not on your PATH after install, symlink the global bin or reload your shell. On macOS with Homebrew you can alternatively run brew install anthropic/tap/claude-code.

Verify the binary runs interactively before touching any config:

claude

You should see the interactive prompt. Exit with Ctrl-C. At this point no model is selected, so Claude Code defaults to the latest generally available model, not Opus 4.8.

Step 2: Provision credentials for Claude Opus 4.8

Create an API key in the Anthropic console with access to the Opus 4.8 model family. The model identifier you will use is claude-opus-4-8 (Anthropic sometimes appends a date suffix like claude-opus-4-8-2025-11; use the exact string your provider expects).

Export the key for the current shell:

export ANTHROPIC_API_KEY="sk-ant-xxxxxxxxxxxxxxxx"

If you prefer a gateway that fronts multiple providers, you can route through an OpenRouter-class proxy. n4n.ai exposes one OpenAI-compatible endpoint covering 240+ models and will automatically fall back when a provider is rate-limited or degraded. Claude Code speaks the Anthropic protocol natively, so you would put a thin translation proxy in front (covered in Step 6).

For the base case, the Anthropic key is sufficient. Store it in your shell profile or a secrets manager; do not commit it.

Step 3: Configure the model in Claude Code

The claude opus 4.8 claude code setup requires pinning the model explicitly. Three mechanisms work, in order of precedence: command-line flag, environment variable, and settings file.

Command line:

claude --model claude-opus-4-8

Environment variable (useful for CI):

export ANTHROPIC_MODEL="claude-opus-4-8"

Persistent project or user config via ~/.claude/settings.json:

{
  "model": "claude-opus-4-8",
  "permissionMode": "default",
  "maxTokens": 8192
}

If both env var and settings exist, the env var wins. I recommend the settings file for local dev because it travels with the repo when placed in .claude/settings.json, keeping the claude opus 4.8 claude code setup reproducible for teammates.

Step 4: Tune context and permissions for agentic coding

Opus 4.8 handles long contexts, but Claude Code will still cap per-call output unless you raise maxTokens. For autonomous refactors, set a higher ceiling:

{
  "model": "claude-opus-4-8",
  "maxTokens": 16384,
  "permissionMode": "bypassPermissions",
  "allowedTools": ["Edit", "Bash", "Read"]
}

bypassPermissions lets the agent run shell commands without prompting—fine in a sandboxed container, dangerous on a laptop with credentials. For daily use, permissionMode: "default" and explicitly approve each tool call.

Add project-specific ignore rules so the agent doesn’t rewrite lockfiles unnecessarily:

{
  "ignorePatterns": ["node_modules/**", "dist/**", "*.lock"]
}

Step 5: Launch and verify the model identity

Start the agent with the pinned model and immediately query its self-knowledge:

claude --model claude-opus-4-8

Inside the REPL:

> /model

The output must list claude-opus-4-8 as the active model. If it shows claude-3-5-sonnet or similar, your env var or settings were overridden.

As a second check, ask the model directly:

What is your exact model identifier and training cutoff?

Opus 4.8 should respond with its own name and a date. This step is the core of a reliable claude opus 4.8 claude code setup: never assume the flag worked.

You can also verify the key and model from outside the REPL with a curl to the Anthropic messages API:

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-opus-4-8",
    "max_tokens": 256,
    "messages": [{"role": "user", "content": "Reply with your model id only."}]
  }'

A 200 with the expected text confirms credentials and model availability.

Step 6: Route through a fallback gateway (optional)

If you run Claude Code in a pipeline and cannot tolerate a single-provider outage, put a translation proxy between the CLI and an OpenAI-compatible gateway. Litellm is the shortest path:

pip install litellm
litellm --model openai/claude-opus-4-8 \
        --api_base https://api.n4n.ai/v1 \
        --api_key "$N4N_API_KEY" \
        --port 4000

This starts a local Anthropic-compatible server that forwards to n4n.ai’s endpoint, which fronts Opus 4.8 and applies automatic fallback when a backend is degraded. Point Claude Code at it:

export ANTHROPIC_BASE_URL="http://localhost:4000"
export ANTHROPIC_API_KEY="dummy"   # litellm handles upstream auth
claude --model claude-opus-4-8

Per-token usage metering from the gateway shows up in your n4n.ai dashboard, and provider cache-control hints are forwarded, so prompt caching still works.

Step 7: Validate end-to-end with a real task

Create a scratch directory and let the agent perform a small, observable change:

mkdir /tmp/opus-test && cd /tmp/opus-test
git init -q
echo "def add(a,b): pass" > math.py
claude --model claude-opus-4-8

Inside the session:

Implement add(a,b) to return the sum. Then run a quick assertion.

Check git diff after the session. You should see a working function and possibly a test command in the history. If the agent edited the file correctly, your claude opus 4.8 claude code setup is verified end to end.

Troubleshooting

401 Unauthorized – Key missing or scoped wrong. Run echo $ANTHROPIC_API_KEY and confirm it matches the console.

404 Model not found – You used claude-opus-4.8 with a dot. Anthropic model IDs use hyphens: claude-opus-4-8.

Context length exceeded – Opus 4.8 supports a large window, but Claude Code’s maxTokens caps output, not input. If you hit input limits, reduce included files via .claude/ignorePatterns.

Base URL ignored – Claude Code only respects ANTHROPIC_BASE_URL when the binary is built with gateway support (recent versions). If it still hits api.anthropic.com, use the litellm proxy on localhost and set the env var explicitly.

What you have now

A pinned, verified Opus 4.8 agent that can be launched with one command, optionally backed by a fallback gateway, and tuned per project for permission and context boundaries. The claude opus 4.8 claude code setup is repeatable via the committed .claude/settings.json, so the next engineer clones the repo and gets the same model without guesswork.