Legioni vs SIMD Agent

Legioni and SIMD Agent are both cli coding agents tracked by AIDiveForge. Below is a side-by-side comparison of pricing, capabilities, platforms, and ownership — sourced from each tool's live website and verified before publishing.

Legioni

The orchestrator receives a plain-language task in opencode, breaks it down, and hands it to a chain of specialist agents — architect, implementer, reviewer, test-strategist — in sequence. Each step feeds the next; the loop closes only when tests pass. The 'lesson promotion' mechanism lets teams encode what they learn into persistent agent behavior, so the same mistake doesn't resurface two projects later. The hard boundary: Legioni runs inside opencode, full stop. If your team is not already on opencode or cannot adopt it, the architecture is irrelevant — there is no standalone path and no API to route through a different runtime.

SIMD Agent

Orbit is an MIT-licensed open-source harness that wraps any JSON-speaking CLI agent — Claude, Codex, Cursor, or otherwise — in a bounded loop: select one task from a dependency-aware backlog, run the agent, gate on real validation (tests, lint, type checks), and write inspectable artifacts before closing the orbit. Every run produces four JSON/markdown files recording what the agent returned, how the output scored against a rubric, whether to accept or iterate, and a human-readable mission log. The harness is intentionally small, so there is precious little abstraction to hide behind — what you see is what runs. Teams with strict audit requirements get durable, reviewable evidence without instrumenting the agent itself. The trade-off is that Orbit is a harness framework, not a turnkey product: you bring the agent, the backlog structure, and the validation suite.

Attribute	Legioni	SIMD Agent
Pricing	Free	Free
Free trial	No	No
Open source	Yes	Yes
Has API	No	No
Self-hosted option	Yes	Yes
Platforms	npm, Node.js	Python 3, Linux, macOS
Pros	Test-driven agent loop closes only when tests pass, so you are not manually checking whether the implementer's output actually works before shipping it to review. Specialist agents handle discrete roles — architecture, implementation, review, test strategy — which means a single task does not collapse into one undifferentiated prompt that loses track of constraints halfway through. Lesson promotion persists learned behaviors across sessions and projects, so teams stop re-encoding the same project rules every time they open a new task. Zero-install path via npx means you can run `legioni init` in a new repo without touching your global Node environment, keeping adoption friction low for the first experiment. MIT license and self-hosted operation mean the agents run entirely within your environment — no usage data leaves to a vendor API beyond whatever opencode itself sends.	Agent-neutral adapter contract, so you can swap Claude for Codex or any other JSON-speaking CLI behind the same harness without rewriting your validation logic or losing artifact continuity. Validation gates block task completion until tests, lint, and type checks pass, which means 'the agent said it worked' is never the acceptance criterion — proof is. Dependency-aware backlog selection keeps each orbit scoped to one task at a time, so the agent cannot drift into adjacent work and leave the codebase in a half-finished state. Structured artifact output per run — four files covering result, evaluation, review recommendation, and progress log — so audit trails and agent comparison experiments run on inspectable data rather than stdout logs. MIT-licensed and self-hostable with no commercial dependency, so the harness can run inside air-gapped or regulated environments where a SaaS agent platform is a non-starter.
Cons	Legioni is a hard dependency on opencode: every agent, every loop, every lesson runs inside opencode's runtime. Teams on Cursor, Cline, or any other AI coding environment cannot use this tool — the only path forward is adopting opencode first, which is a separate adoption decision with its own trade-offs. The project's public repository shows five commits and a small star count, which means edge cases in the agent loop, lesson promotion conflicts, and stack detection failures are under-documented and under-reported. Teams hitting unexpected behavior have no community issue history to search and no support channel beyond filing a GitHub issue themselves. Lesson promotion is a manual, explicit action — the agents do not automatically surface or apply learned behaviors without team intervention. Projects where nobody curates the promoted lessons see no compounding benefit across sessions, which makes the core differentiating feature opt-in rather than default.	Orbit produces no UI — review artifacts are JSON and markdown files on disk. Teams where product managers or compliance officers need to review agent work without opening a terminal hit this wall immediately and end up building a separate reporting layer. The validation gates are only as strong as the suite you bring: a codebase with no tests, no lint config, and no type checks gives Orbit nothing to gate on, which means the bounded-loop guarantee collapses to 'the agent returned output' — the same problem Orbit exists to solve. Backlog and task structure require manual definition in a format the harness expects; there is no backlog ingestion from issue trackers, project management tools, or CI systems. Teams running high-velocity sprints from Jira or Linear spend engineering time on a translation layer, and when that overhead compounds, they switch to an agent platform with native integrations. There is no API surface — the tool is CLI-only — so embedding Orbit into a larger automated pipeline (CI/CD, event-driven triggers, multi-repo workflows) requires shell scripting around the harness rather than programmatic control.

Bottom line

Legioni and SIMD Agent are closely matched on pricing model, openness, and API availability — pick by feature set and platform support in the table above.

Frequently asked questions

What is the difference between Legioni and SIMD Agent?

Legioni is Free and open source, while SIMD Agent is Free and open source. Compare pricing, free trial, API, platforms, and pros/cons in the table above on AIDiveForge.

Is Legioni better than SIMD Agent?

It depends on your workflow. Use the side-by-side attributes (pricing, open source, API, self-hosted, platforms) to decide. AIDiveForge does not rank a universal winner — we publish verified facts so you can choose.