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

# Anthropic (Claude)

> How to configure Anthropic (Claude) for use with Cyrus

Set up Anthropic so Cyrus can use Claude to reason about code changes, plans, and tasks. You can connect via an **API Key** or a **Subscription**.

Once configured, you can make Claude your [default model provider](/providers/default-model-provider).

***

## Open the Anthropic configuration

<Steps>
  <Step title="Go to Integrations">
    Navigate to [app.atcyrus.com/settings/integrations](https://app.atcyrus.com/settings/integrations).
  </Step>

  <Step title="Open the configuration modal">
    Find the **Claude** tile, click the **dropdown** on the right side of the tile, and select **Configure**.
  </Step>

  <Step title="Choose your authentication method">
    At the top of the configuration modal you'll see a dropdown — pick **API Key** or **Subscription** depending on how you'd like to authenticate.
  </Step>
</Steps>

***

## Supported models

Cyrus supports the following Claude models. Use the alias as a Linear label or in a `[model=...]` description tag — see [Default Model Provider](/providers/default-model-provider) for syntax.

| Alias    | Model             | Notes                                                |
| -------- | ----------------- | ---------------------------------------------------- |
| `fable`  | Claude Fable 5    | Highest capability. Falls back to Opus, then Sonnet. |
| `opus`   | Claude Opus 4.8   | Default.                                             |
| `sonnet` | Claude Sonnet 4.6 | Balanced quality and speed.                          |
| `haiku`  | Claude Haiku 4.5  | Fast and cost-efficient.                             |

If no model label is set, Cyrus uses **`opus`** and falls back to **`sonnet`** on retry. When `fable` is selected, Cyrus runs `claude-fable-5` and automatically falls back to **`opus`**, then **`sonnet`**.

[Claude Fable 5](https://www.anthropic.com/news/claude-fable-5-mythos-5) is Anthropic's most capable Claude model. You can make it your team's default Claude model in [Behaviours settings](https://app.atcyrus.com/settings/behaviours), or try it on a single issue by adding the `fable` label before assigning the issue to Cyrus.

You can also pass a fully-qualified Anthropic model ID (e.g. `claude-fable-5` or `claude-opus-4-8`) in a `[model=...]` tag.

***

## API key setup

### Option A: use `claude setup-token`

You can generate a token through the CLI:

```bash theme={null}
claude setup-token
```

This command will output a token. Copy it, then paste it into the Cyrus Claude configuration modal (with **API Key** selected).

<Warning>
  Be careful to remove any extra whitespace or newlines from the token before pasting — trailing spaces or line breaks can cause "bad key" errors.
</Warning>

### Option B: create a key via the Anthropic Console

<Steps>
  <Step title="Sign in to Anthropic">
    Go to [console.anthropic.com](https://console.anthropic.com/) and sign in. If you don't have an account, create one first.
  </Step>

  <Step title="Open the API Keys page">
    Click **API Keys** in the left sidebar, or go directly to [console.anthropic.com/settings/keys](https://console.anthropic.com/settings/keys).
  </Step>

  <Step title="Create a new key">
    Click **Create Key**. Give it a name like `cyrus` to identify it later.
  </Step>

  <Step title="Copy the key">
    Your key will be shown once. Copy it immediately — you won't be able to view it again after closing the dialog.
  </Step>

  <Step title="Paste it into Cyrus">
    Back in the Cyrus Anthropic configuration modal (with **API Key** selected), paste your key and save.
  </Step>
</Steps>

<Warning>
  If you lose your API key, you'll need to generate a new one. Anthropic does not allow you to view existing keys after creation.
</Warning>

### Add billing

Anthropic API keys require a billing method. If you haven't set one up:

1. Go to [console.anthropic.com/settings/billing](https://console.anthropic.com/settings/billing)
2. Add a payment method
3. Optionally configure spend limits

***

## Troubleshooting

**"Invalid Claude API key" error**

* Make sure you copied the full key (it starts with `sk-ant-`)
* Verify the key hasn't been disabled in the Anthropic console

**"Insufficient credits" error**

* Check your billing status at [console.anthropic.com/settings/billing](https://console.anthropic.com/settings/billing)
* Ensure your account has available credits or an active payment method

***

## Next steps

To make Claude the provider Cyrus uses for every issue, see [Default Model Provider](/providers/default-model-provider).

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