Claude Code Setup Guide: How to Configure Custom API Access in 2026

Claude Code has become one of the most powerful AI-powered development tools in 2026, but many developers outside the US face a common problem: Anthropic requires a US-issued credit card for API access, and direct API calls from certain regions can be unreliable.

The good news? You can configure Claude Code to use a custom API endpoint that solves both problems. This guide walks you through the complete setup process in 2026.

What You'll Need

Before starting, make sure you have:

• Claude Code installed (download from the official Anthropic website)
• An OpenAI-compatible API relay service (we'll cover options below)
• 5 minutes for configuration

Step 1: Choose Your API Relay Service

An API relay acts as a bridge between Claude Code and Anthropic's servers. The relay handles authentication, routing, and billing, while you get full access to Claude Opus 4.8, Sonnet 5, and other models.

When choosing a relay, look for:

• OpenAI-compatible endpoint — Claude Code expects the standard chat/completions format
• Prompt caching support — Can cut your costs by 70-90% on repetitive requests
• No credit card required — Alternative payment methods like Alipay
• Lower pricing — Some relays offer volume discounts below Anthropic's official rates

For example, Safa API provides all of the above, plus a unified endpoint for Claude, GPT, and Gemini models. You can register at aisafa.xyz/register and start with as little as ¥10 CNY via Alipay.

Step 2: Set the ANTHROPIC_BASE_URL Environment Variable

Claude Code reads API configuration from environment variables. The key variable is ANTHROPIC_BASE_URL, which tells Claude Code where to send requests.

On macOS/Linux

export ANTHROPIC_BASE_URL="https://api.example.com/v1"
export ANTHROPIC_API_KEY="your-api-key-here"

To make this permanent, add these lines to your ~/.zshrc or ~/.bashrc:

echo 'export ANTHROPIC_BASE_URL="https://api.example.com/v1"' >> ~/.zshrc
echo 'export ANTHROPIC_API_KEY="your-api-key-here"' >> ~/.zshrc
source ~/.zshrc

On Windows

Open PowerShell and run:

[System.Environment]::SetEnvironmentVariable('ANTHROPIC_BASE_URL', 'https://api.example.com/v1', 'User')
[System.Environment]::SetEnvironmentVariable('ANTHROPIC_API_KEY', 'your-api-key-here', 'User')

Restart Claude Code after setting these variables.

Step 3: Verify the Connection

Open Claude Code and start a new chat session. Ask a simple question like "What models can you access?" If the configuration is correct, Claude will respond normally.

To confirm which endpoint is being used, check the network tab in your system monitor or firewall logs. You should see requests going to your custom base URL instead of api.anthropic.com.

Cost Optimization Tips

Once you have Claude Code running through a custom endpoint, you can reduce costs significantly:

1. Enable Prompt Caching

Most relays automatically support Anthropic's prompt caching feature. When you send repeated requests with the same system prompt or context, the relay caches the input tokens and charges only 10% for cached reads. This works especially well for:

• Codebase analysis with large context windows
• Repetitive debugging sessions
• Multi-file refactoring tasks

2. Use Model Tiers Strategically

Not every task needs Opus 4.8. For simpler tasks like code formatting, docstring generation, or quick explanations, Claude Sonnet 5 costs 75% less while maintaining excellent quality.

3. Monitor Your Usage

Most relay services provide a usage dashboard showing token consumption by model and date. Check it weekly to identify expensive patterns.

Common Issues and Fixes

"API key invalid" Error

Double-check that you're using the API key from your relay service, not your Anthropic Console key (if you have one). They're not interchangeable.

"Connection timeout" or Slow Responses

Some relays route traffic through multiple regions. If you're experiencing latency, check if your relay offers regional endpoints (e.g., Asia-Pacific vs US-West) and switch to the closest one.

"Model not found" Error

Verify that your relay supports the exact model name Claude Code is requesting. Most relays use [REDACTED] or [REDACTED], but naming can vary. Check your relay's documentation for the supported model list.

Why Use a Custom Endpoint Instead of Direct Access?

Even if you have an Anthropic API account, a relay service can still offer advantages:

• Lower total cost — Volume discounts and competitive pricing can beat official rates
• Unified billing — One account for Claude, GPT, and Gemini instead of three separate subscriptions
• Better payment options — Alipay, WeChat Pay, and other regional methods
• Prompt caching at full discount — Not all Anthropic tiers enable full caching benefits

For developers in regions where Anthropic's direct service is restricted or requires complicated verification, a relay is often the only practical option.

Next Steps

Once Claude Code is configured with your custom endpoint, you can explore advanced features like:

• Subagents for parallel multi-file editing
• Function calling for database queries and API integrations
• Computer Use API for browser and desktop automation (experimental in 2026)

All of these work normally through a properly configured relay, with no changes needed to your Claude Code setup.

Frequently Asked Questions

Can I switch back to the official Anthropic API later?

Yes. Just unset the ANTHROPIC_BASE_URL variable and use your official Anthropic API key. Claude Code will automatically revert to api.anthropic.com.

Does this work with Claude Code on all platforms?

Yes. The ANTHROPIC_BASE_URL environment variable is cross-platform and works on macOS, Linux, and Windows. The only difference is how you set the variable (see Step 2 above).

Will I lose access to new models when they're released?

Most relay services add new Claude models within hours of Anthropic's official release. If you need bleeding-edge access on day zero, check your relay's changelog or subscribe to their update notifications.