> ## 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.

# Default Model Provider

> How to change the default model provider used for every issue and agent run

Once you've configured one or more [model providers](/providers/anthropic), you can choose which one Cyrus uses by default for every Linear issue and `agent run`.

***

## Change the default model provider

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

  <Step title="Select a provider">
    Find the **Default Model Provider** dropdown and select the provider you want Cyrus to use by default (e.g. Claude, OpenAI/Codex, Cursor).
  </Step>
</Steps>

This setting applies globally — every new issue and `agent run` will use the selected provider unless overridden per-issue.

***

## Override the provider per issue

You can override the default provider for a specific issue in two ways:

### Using an inline tag in the issue description

Add one of the following tags anywhere in your Linear issue description:

```text theme={null}
[agent=claude]
[agent=codex]
[agent=cursor]
[agent=gemini]
```

### Using a Linear label

Apply the provider name as a **label** on the issue:

```text theme={null}
claude
codex
cursor
gemini
```

***

## Override the model per issue

You can also override the specific **model** (not just the provider) for a given issue, either with a `[model=...]` description tag or a Linear label of the same name.

### Supported models by provider

**Claude** ([Anthropic](/providers/anthropic))

| Alias    | Model             |
| -------- | ----------------- |
| `fable`  | Claude Fable 5    |
| `opus`   | Claude Opus 4.8   |
| `sonnet` | Claude Sonnet 4.6 |
| `haiku`  | Claude Haiku 4.5  |

Default: `opus`. Fallback: `sonnet`. When `fable` is selected, the fallback chain is `fable` → `opus` → `sonnet`.

You can also save `fable` as your team's default Claude model from the [Behaviours settings](https://app.atcyrus.com/settings/behaviours) page.

**Codex** ([OpenAI](/providers/openai))

| Model           | Notes                                                                    |
| --------------- | ------------------------------------------------------------------------ |
| `gpt-5.5`       | Latest frontier model. Unifies Codex and non-Codex — no `gpt-5.5-codex`. |
| `gpt-5.3-codex` | Default.                                                                 |
| `gpt-5.2-codex` | Automatic fallback.                                                      |
| `gpt-5-codex`   | Earlier Codex generation.                                                |
| `gpt-5`         | Earlier non-Codex GPT-5.                                                 |

Any `gpt-*-codex` or `gpt-*` name is accepted, so newer Codex releases can be selected by name.

**Gemini**

| Model                   | Notes                                |
| ----------------------- | ------------------------------------ |
| `gemini-2.5-pro`        | Default. Alias: `gemini-2.5`.        |
| `gemini-2.5-flash`      | Faster, lighter.                     |
| `gemini-2.5-flash-lite` | Lightweight.                         |
| `gemini-3-pro-preview`  | Aliases: `gemini-3`, `gemini-3-pro`. |

Default: `gemini-2.5-pro`. Fallback: `gemini-2.5-flash`.

**Cursor** ([Cursor](/providers/cursor))

Runs `composer-2`. Per-issue model overrides are not currently exposed.

### Examples

Inline tag:

```text theme={null}
[model=fable]
[model=opus]
[model=gpt-5.3-codex]
[model=gemini-2.5-pro]
```

Linear label:

```text theme={null}
fable
opus
gpt-5.3-codex
gemini-2.5-flash
```

If a `[model=...]` is set without an `[agent=...]`, Cyrus infers the provider from the model name. For more, see [Labels and Routing](/labels-and-routing#optional-override-the-ai-model).

***

## Agent sessions

The agent (provider) cannot be switched **within** an active agent session. If you need to use a different provider on the same issue, a new agent session will be spawned with the selected agent.

***

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