Exo on a MicroVM: The Harness That Rewrites Itself

Most agents can "self-improve" in the small ways: a memory file, a skills directory, a prompt tweak.

Exo can rewrite the harness it is running on.

Not as a stunt. As the architecture. A trusted substrate (event log, secrets, sandboxes) sits underneath. Everything the agent is allowed to change — prompts, tools, executor policy, even TypeScript harness code — sits above it. Failed experiments rewind. Successful ones stick. Alex Krentsel has described the split as giving the model a body it can actually operate on.

That is a different product from a coding CLI. It is also a different persistence problem: if the install tree lives on an ephemeral rootfs, every reprovision throws away the self-improvements. So on jurniti the tree lives on persist.

Run Exo on a jurniti microVM

The laptop problem

A recursive harness on the machine that holds your keys is a category error.

The agent has a shell and can edit its own code.
You want that loop to keep running when the laptop lid closes.
You want tomorrow's SELF.md to still be yesterday's work, not a fresh clone.

Exo's own docs start from "one setup script to a running agent." Setup on a laptop still leaves you babysitting a process. The managed version is not more UI. It is the same harness, left on, isolated, with a disk that outlives the process.

What we actually run

jurniti gives Exo its own computer — a Firecracker microVM. Not a container. Not a shared kernel.

On provision you get:

A fresh Ubuntu guest with exo on PATH. The pinned checkout, toolchains, and built binaries are pre-baked.
A live in-browser terminal. Write YOUR key to ~/exo/byok.env, then run exo.
Persist at ~/exo — SELF.md, the TypeScript harness the agent rewrites, scheduler state. A reprovision keeps them.
Docker in-guest as the default sandbox backend. Nested Firecracker is not required and is not enabled.

BYOK throughout. We never proxy model spend. The bake-time dotenv is a structural placeholder so unattended install cannot hang on a secret prompt. It is not a real key, and jurniti env set writes the BYOK file that wins.

The relay stays off

Exo can speak through a vendor ExoChat relay. A managed box must not ship that on by default, and a fork must not inherit the original owner's channel identity.

The shipped config names no vendor host. The wrapper launches --template minimal. Capture drops .exo/ adapter sessions and the host secret store. If you turn the relay on, that is your data and your choice — it still will not ride a public fork.

Snapshot it — later

Public templates for Exo are vetoed until a live capture canary has proven the scrub: no key, no ExoChat session, no canary in a kept file. A forker executing another tenant's rewritten harness is a supply-chain surface this gallery has never had. The veto stays until that evidence exists.

Honest limits

Rolling upstream. No tags, no releases. package.json says 0.1.0 forever. We pin a commit and bump by hand.
Terminal-first. There is no guest-bound dashboard to proxy. You work in the in-browser terminal.
No free tier. From $25/mo. The de-risk is a 30-day money-back guarantee on your first purchase, not a trial.

Get the box

Pick a plan, choose Exo, pay. The VM is up in a few minutes. Then:

printf 'OPENAI_API_KEY=sk-your-key\n' > ~/exo/byok.env && chmod 600 ~/exo/byok.env
exo

Frequently asked questions

What is Exo?

Exo is an MIT-licensed agent harness from exoharness. The agent can see its own code and runtime logs and incrementally rewrite prompts, tools, and harness policy above a trusted substrate it cannot alter. The event log is the canonical history.

Where do self-improvements live?

On persist. Exo's launcher derives its root from its own location, so the checkout, SELF.md, and .exo/ state all live under ~/exo on the persist disk. A reprovision keeps them. They are not wiped with the rootfs.

How do I authenticate?

BYOK. Write your OpenAI or OpenRouter key into ~/exo/byok.env, then run `exo`. The bake-time dotenv is a placeholder so install cannot hang on a secret prompt. It is not your key.

Does Exo phone home to a vendor relay?

Not in the shipped config. The vendor ExoChat relay is off, the chat base URL is a non-vendor override, and a capture drops relay identifiers so a fork never inherits the original owner's channel.