Environment Variables

Environment variables available in agent bash commands and hooks

The following environment variables are available in all agent bash tool executions, including init hooks.

Available Variables

Variable	Description
MUX_PROJECT_PATH	Absolute path to the project root on the local machine. Always refers to your local project path, even on SSH workspaces.
MUX_RUNTIME	Runtime type: "local", "worktree", "ssh", or "docker"
MUX_WORKSPACE_NAME	Name of the workspace (typically the branch name)
MUX_MODEL_STRING	Model identifier (e.g., "anthropic:claude-sonnet-4-20250514")
MUX_THINKING_LEVEL	Reasoning level: "off", "low", "medium", "high", or "xhigh"
MUX_COSTS_USD	Cumulative session costs in USD, formatted to 2 decimal places (e.g., "1.23")

Usage Example

#!/usr/bin/env bash

echo "Project: $MUX_PROJECT_PATH"
echo "Runtime: $MUX_RUNTIME"
echo "Workspace: $MUX_WORKSPACE_NAME"
echo "Model: $MUX_MODEL_STRING"
echo "Thinking: $MUX_THINKING_LEVEL"
echo "Costs: \$${MUX_COSTS_USD:-0.00}"

# Runtime-specific behavior
if [ "$MUX_RUNTIME" = "ssh" ]; then
  echo "Running on SSH remote"
elif [ "$MUX_RUNTIME" = "docker" ]; then
  echo "Running in Docker container"
else
  echo "Running locally"
fi

Use Cases

• PR footers: Include model and cost information in automated PR descriptions
• Conditional logic: Adapt scripts based on runtime environment
• Logging: Track which model and settings were used for a task
• Cost monitoring: Check cumulative costs before expensive operations