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

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Available Variables

VariableDescription
MUX_PROJECT_PATHAbsolute path to the project root on the local machine. Always refers to your local project path, even on SSH workspaces.
MUX_RUNTIMERuntime type: "local", "worktree", "ssh", or "docker"
MUX_WORKSPACE_NAMEName of the workspace (typically the branch name)
MUX_MODEL_STRINGModel identifier (e.g., "anthropic:claude-sonnet-4-20250514")
MUX_THINKING_LEVELReasoning level: "off", "low", "medium", or "high"
MUX_COSTS_USDCumulative session costs in USD, formatted to 2 decimal places (e.g., "1.23")

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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

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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