MCP_CONNECTION_NONBLOCKING

Updated October 13, 2026 by Alex Sorokoletov

MCP_CONNECTION_NONBLOCKING is a Claude Code environment variable: Make MCP connections non-blocking. Its release history is not tracked here. It is listed in the official reference.

Status	Present in v2.1.294
Category	Network and proxy
Official docs	Listed

How to set it

For one session, export it in the shell that starts Claude Code:

export MCP_CONNECTION_NONBLOCKING=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "MCP_CONNECTION_NONBLOCKING": "<value>"
  }
}

Release notes that mention it

Claude Code v2.1.89 — 4 New Environment Variables: Agent Cost Steering, Session Resume Controls, and 50% StructuredOutput Fix

Related variables

MCP_REMOTE_SERVER_CONNECTION_BATCH_SIZE: Remote MCP connection batch size.
MCP_SERVER_CONNECTION_BATCH_SIZE: Concurrent MCP server connections.
CLAUDE_CODE_DISABLE_MTLS_RELOAD_ON_STALE_CONNECTION
CLAUDE_CODE_MCP_SERVER_URL: The companion to MCP_SERVER_NAME, providing the server endpoint URL.
CLAUDE_CODE_MCP_TOOL_IDLE_TIMEOUT
MCP_CONNECT_TIMEOUT_MS
MCP_TIMEOUT: MCP server connection timeout.
MCP_TOOL_TIMEOUT: Individual MCP tool execution timeout.

Frequently asked questions

What does MCP_CONNECTION_NONBLOCKING do?

Make MCP connections non-blocking

Which Claude Code version has MCP_CONNECTION_NONBLOCKING?

Its release history is not tracked here.

How do I set MCP_CONNECTION_NONBLOCKING?

Export it before starting Claude Code (export MCP_CONNECTION_NONBLOCKING=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.

All variables, searchable: Claude Code environment variables.