> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pentagon.run/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent Runtimes

> Claude Code, Codex, and how to pick the right one for each agent

# Agent Runtimes

Every Pentagon agent runs on top of a **coding-agent CLI** installed on your Mac. Pentagon supports two runtimes today: **Claude Code** (Anthropic) and **Codex** (OpenAI). You can install one or both, and you can pick which one each agent uses.

## Why two runtimes?

Different models are good at different things. Picking the runtime per agent lets you:

* Use Claude for one agent and Codex for another — same canvas, same team
* Match the model to the work (long-context reasoning, tool use, coding speed, cost)
* Avoid being locked into a single vendor's pricing or availability

## Installing a runtime

You install the CLI yourself — Pentagon doesn't ship the binaries. From a terminal:

```bash theme={null}
# Claude Code
curl -fsSL https://claude.ai/install.sh | bash
claude        # sign in

# Codex
# Install via the official Codex distribution, then:
codex login   # sign in
```

Pentagon detects both CLIs on launch and again whenever you open the Create Agent screen — so a newly-installed CLI shows up immediately.

## Picking a runtime for an agent

The runtime is determined by the **model** you select for the agent. Each model in Pentagon's model picker is tagged with its runtime:

* **Claude Opus / Sonnet / Haiku** → runs on Claude Code
* **GPT-5 family** → runs on Codex

When you change the model in the agent's **Settings → About** section (or at creation time), Pentagon switches the runtime automatically. There's no separate runtime toggle.

## Checking what's available

Open **Settings** and look for the runtime section. Pentagon shows the status of each CLI:

* **Ready** — installed and signed in
* **Missing** — not installed yet
* **Sign in** — installed but not authenticated
* **Optional** — you already have the other one, so this is fine to skip

You need Git and at least one runtime ready to spawn local agents. The first-run setup flow checks this before letting you create your first agent.

## How agents run

Agents run on your Mac — Pentagon spawns a local CLI process for each turn. Each agent uses its own clone of your repo (on its own git branch) so they don't step on each other.

<Card title="Next: Spawning Agents" icon="robot" href="/agents/creating-agents">
  Build your first agent.
</Card>