Last Light vs. Archon: Harness Builder or Maintenance Service?

The short version

Archon bills itself as "the first open-source harness builder for AI coding", and it is the most architecturally similar tool on this site. Both projects borrow the same core idea: workflows as code, dispatched from wherever you happen to be.

The split is what sits inside the workflow. Archon orchestrates external agent CLIs, so you bring your own coding agent and it runs wherever you point it. Last Light has its own integrated runtime with model routing built in, and it runs that runtime entirely inside the sandbox boundary. Archon is the more agent-agnostic of the two; Last Light is the more self-contained.

The second split is intent. Archon is about dispatch: fire off many parallel runs. Last Light is about maintenance: a standing service that triages, reviews and reports on its own, with humans gating the interesting moments.

Side by side

	Last Light	Archon
What runs the agent	Its own integrated runtime (agentic-pi / pi-ai)	Your existing agent CLIs (Claude Code, Codex, and so on)
Isolation	Docker / micro-VM sandbox, default-deny egress firewall	Per-run Git worktrees
Framing	Autonomous repo maintenance, running on its own	Developer dispatch: send work from anywhere
Channels	GitHub webhooks, Slack, cron, CLI, dashboard	Terminal, Slack, Telegram, GitHub comments, web
Parallelism	Sequential per repo, gated	Fan-out across worktrees
Workflows shipped	Triage, review, build, security, health, chat	You build them
Agent-agnostic	No: the runtime is part of the system	Yes, that is the point
Licence	MIT, free	Open source, free

The three real differences

What runs the agent. Archon is a harness that drives agent CLIs you already use, which makes it flexible and keeps you on tools you know. Last Light bakes the runtime in, which makes it more opinionated but means the whole agent sits inside one boundary.
Isolation. Archon isolates parallel runs in per-run Git worktrees: light, collision-free, and excellent for fan-out. Last Light isolates in a Docker or micro-VM sandbox with a default-deny egress firewall and downscoped per-run tokens. That is heavier, but it is a real network and permission boundary. It is also the whole agent in the box, not just its tools: reasoning, bash, file I/O and egress all behind one perimeter, so a prompt injection has nowhere to escape to rather than relying on each tool call to route itself through a sandbox.
Intent. Archon wants you to dispatch work from anywhere and run many agents at once. Last Light wants to be left alone to look after a repository, and to interrupt you only at an approval gate.

Which should you pick?

Choose Archon when

you want a lightweight, agent-agnostic harness to dispatch parallel coding runs across worktrees from many channels, driving whatever CLI agent you already use.

Choose Last Light when

you want a self-contained repo-maintenance service with its own runtime, a hardened sandbox, egress and token boundary, and a built-in suite of triage, review, health and security workflows.

Honestly, if you like one project's philosophy you should look at the other. They are solving adjacent problems from the same starting idea.

Last Light vs. Archon

The short version

Side by side

The three real differences

Which should you pick?

Compare against something else