Muse Code Delegation

Overview

Muse Code is Meta's terminal coding agent, released August 2026 and built on Muse Spark 1.2. It runs either as an interactive TUI or as a one-shot headless command, and the headless form is what delegation uses.

The binary is muse. Meta publishes no npm or PyPI package for it: the documented install is a script served from Meta's own domain.

When To Use

• delegation-core selected muse for the task
• Repository-scale reading where Muse Spark 1.2's 1M-token context helps
• Work that should run unattended, since muse exec is designed for CI

When NOT To Use

• META_API_KEY is unset and the run cannot be interactive
• A specific model must be selected. Meta documents no --model flag for exec, so the CLI default stands
• Structured output is required. No output-format flag is documented for exec

Prerequisites

Installation

curl -fsSL https://dev.meta.ai/install.sh | sh

This pipes a remote script into a shell. Read https://dev.meta.ai/docs/muse-code before running it. The guided installer offers the same command and shows its source first:

make -C plugins/conjure delegate-setup

Authentication

Meta documents the environment variable as the CI path:

export META_API_KEY="<your-key>"
muse exec "Run the test suite and summarize failures."

A bare muse prompts for browser sign-in on first run, which is not usable unattended. There is no muse auth status command, so the service declares an empty auth probe and verification checks META_API_KEY instead.

Quick Start

Using the shared delegation executor

uv run python scripts/delegation_executor.py muse "Summarize this module" \
  --files src/

Through the Makefile

make -C plugins/conjure delegate-muse PROMPT='Explain this design'

Direct CLI usage

muse exec "Explain the retry logic in this package"

Smart Delegation

muse declares the strengths code_execution and large_context, and ranks behind gemini, qwen, minimax and glm in the candidate order. It declares no model ids, so smart_delegate leaves model selection to the CLI rather than passing a flag Meta does not document.

Muse-Specific Details

Property	Value
Binary	muse
Headless form	muse exec <prompt>
Prompt delivery	positional, no flag
Version probe	muse --version
Auth probe	none published
Auth	META_API_KEY
File context	inlined, no @path syntax

The prompt is positional. A command ending in a flag would consume the prompt as that flag's value, which is why the service config sets prompt_flag=None and the War Room expert's command ends at muse exec.

Two claims circulating in third-party guides are not in Meta's own documentation and are not relied on here: a --json flag streaming JSONL events to stdout, and muse auth set --api-key-stdin. The confirmed JSONL reference is to on-disk session logs. Treat both as unverified until Meta documents them.

Exit Criteria

• muse resolves on PATH and muse --version answers
• META_API_KEY is set, or the operator accepted an interactive sign-in
• The built command is muse exec <prompt> with the prompt as the final argument and no prompt flag before it
• File context was inlined into the prompt rather than passed as @path references
• Output saved to delegations/muse/YYYYMMDD_HHMMSS.md
• This skill ran because delegation-core selected muse, not by default