---
title: Authentication
description: Connect Atomic to a provider with a subscription login or an API key.
---

# Authentication

**Outcome:** Atomic can reach a model provider and `/model` lists models you can select.

**Prerequisites:** [Installation](/getting-started/installation) is complete.

## Authenticate

Atomic can use subscription providers through `/login`, or API-key providers through environment variables or the auth file.

### Option 1: subscription login

Start Atomic and run:

```text
/login
```

Choose **Use a subscription**, then select a provider. Built-in subscription logins include Claude Pro/Max, ChatGPT Plus/Pro (Codex), and GitHub Copilot.

### Option 2: API key

Set an API key before launching Atomic:

```bash
export ANTHROPIC_API_KEY=sk-ant-...
atomic
```

You can also run `/login`, choose **Use an API key**, then select a provider to store the key in `~/.atomic/agent/auth.json`.

See [Providers](/providers) for all supported providers, environment variables, and provider-specific setup.

## Verify authentication

Start Atomic in any directory and run:

```text
/model
```

The model picker should list selectable models for the provider you configured, with the active one marked. If it is empty or Atomic reports no configured provider:

- Re-run `/login`.
- If using an API key, confirm its environment variable is exported in the shell that launched Atomic.

`/login` opens **Select authentication method:**. Choose **Use a subscription** or **Use an API key** to see the corresponding provider picker and credential-configuration status. That status can reflect stored, environment, runtime, or configuration credentials; it does not test connectivity or prove that a provider will accept a request. OAuth sign-ins that are not backed by a subscription are labeled **account** in the provider pickers and status. Cancelling a sign-in returns to the menu you started it from.

Select a model with `/model`, then send a short prompt such as `Reply with hello.` A successful response confirms access for that request. If it fails, check the reported authentication, quota, model-access, or network error before retrying. A configured credential or a listed model alone does not prove access.

## Next step

Continue to [First session](/getting-started/first-session).