Reasoning

Reasoning levels control how much "thinking" a model does before responding. Models that support reasoning (detected from OpenRouter /v1/models metadata) can be configured with different effort levels.

Levels

For models that report reasoning as a binary toggle (on/off without effort levels), the options are simply off and on.

Setting the Level

CLI

cast -r high "refactor this function"
cast --reasoning medium "explain the session module"

Interactive

/reasoning

Opens a picker if the model supports reasoning controls. If the provider doesn't expose reasoning metadata, a message explains that the model uses its own default.

Saved

The reasoning level is saved to ~/.cast/settings.json per model. Switching models triggers a new reasoning selection if the new model supports different options.

How Reasoning Metadata is Discovered

cast fetches the model list from your provider's /v1/models endpoint. OpenRouter-compatible providers include a reasoning field per model:

{
  "id": "qwen/qwen3-235b-a22b",
  "reasoning": {
    "mandatory": false,
    "default_enabled": true,
    "supported_efforts": ["high", "medium", "low"],
    "default_effort": "medium"
  }
}

cast reads this metadata to determine:

• Whether the model supports reasoning at all
• Whether it's a binary toggle or supports effort levels
• Which efforts are available
• What the default is

No vendor detection, no overrides — the API tells cast everything.

Think Block Parsing

Some models (Qwen, DeepSeek) output reasoning in <think> blocks rather than through a structured API field. cast parses these blocks automatically:

<think>
Let me analyze this step by step...
</think>

Here's my analysis...

The thinking content is displayed separately in the TUI and excluded from the main response.

Provider Behavior

When reasoning is set to off, cast sends reasoning: { enabled: false } explicitly. Some models (like OpenRouter's default_enabled: true ones) reason by default when the key is omitted — an empty body doesn't turn reasoning off.

When the provider doesn't report reasoning capabilities (unknown), cast sends no reasoning params, letting the provider use its own default.