Claude Code: Unable to connect to API. Check your internet connection

What it means

The TCP connection to the API failed or never completed. Coded variants include Connection dropped (ECONNRESET), Can't reach the API server - check your internet or DNS (ENOTFOUND), and Couldn't connect through your proxy (ERR_PROXY_TUNNEL). Older versions showed API Error (Connection error.) or Unable to connect to API (ECONNREFUSED).

Causes

• No internet access
• A VPN that blocks api.anthropic.com
• A required corporate proxy that is not configured
• A leftover ANTHROPIC_BASE_URL pointing at a local proxy or gateway that is no longer running
• An unreachable nameserver in /etc/resolv.conf on Linux and WSL
• Stale VPN utun interfaces on macOS, or Docker Desktop intercepting outbound traffic

How to fix it

1. 1
   Fix 1.

   Confirm you can reach the API host from the same shell (on Windows PowerShell use curl.exe).

   Terminal

   Copy

   curl -I https://api.anthropic.com

2. 2
   Fix 2.

   If you are behind a corporate proxy, set HTTPS_PROXY before launching Claude Code, and ensure your firewall allows the hosts in Network access requirements.

3. 3
   Fix 3.

   Check whether ANTHROPIC_BASE_URL is set in your shell or the env block of your settings files; remove a leftover value and start Claude Code from a new terminal.

   Terminal

   Copy

   echo $ANTHROPIC_BASE_URL

4. 4
   Fix 4.

   Intermittent failures are retried automatically; v2.1.198 made transient errors like ECONNRESET retry with backoff instead of failing the turn.