# Engines

> What runs the agents, what it needs, who pays, and what it can touch.

An **engine** is what runs an agent: it starts the agent, sends it a request, and reports what it did. Solipsist's
agents run on one engine today, [Pi](https://solipsist.sh/docs/engines/pi/), an open-source coding agent that runs inside the Solipsist
process. Pi calls the model you connected: [OpenRouter](https://solipsist.sh/docs/start/openrouter/), a provider you logged in to, or a
[model on your own computer](https://solipsist.sh/docs/start/local-models/).

| | Pi |
|---|---|
| Needs | A model: an OpenRouter key, or a login saved in Pi, or a provider in Pi's `models.json` |
| Who pays | You, to the provider you chose. Nothing goes through Solipsist |
| Reports cost | Yes. A run's cost counts toward the [spending limits](https://solipsist.sh/docs/agents/how-agents-work/#spending-limits) (a local model reports $0) |
| Confined | No. Its shell runs commands as you; only its `write` and `edit` tools are limited to the images folder |
| Chat | Yes: [chat](https://solipsist.sh/docs/agents/chat/) with the agent behind a request, and the page-wide chat |
| Steering | Yes: a message sent while it is answering is read after its current step |
| Keeps its conversation | Yes: an agent that finished waits five minutes, then sleeps, and wakes with everything it knew |

## What "confined" means

An agent can run commands on your computer. An engine is **confined** when what it runs can only write to the images
folder and can't reach the network beyond your own computer. Pi isn't: its shell can do anything you can, so treat a
request the way you would treat running Pi in a terminal in that folder. Pi's `write` and `edit` tools are limited to
the images folder by Solipsist, and you can shorten the list of tools with [`pi.tools`](https://solipsist.sh/docs/engines/pi/#tools).

## Choosing the model

Each page has its own model, set in the [agent panel](https://solipsist.sh/docs/reference/agent-panel/). A model is written as
`<engine>:<model>`, for example `pi:openrouter/~deepseek/deepseek-flash-latest`. A request keeps the agent that made it
and its model, so asking again and chatting go back to the same one. See
[Connect a model](https://solipsist.sh/docs/start/connect-a-model/#choosing-the-model).

## If something doesn't work

[When it goes wrong](https://solipsist.sh/docs/engines/when-it-goes-wrong/) lists the messages you can see and what fixes each.

Source: https://solipsist.sh/docs/engines/overview/