https://openrouter.ai/docs/use-cases/reasoning-tokens#controlling-reasoning-tokens

You can control reasoning tokens in your requests using the reasoning parameter:

{
  "model": "your-model",
  "messages": [],
  "reasoning": {
    // One of the following (not both):
    "effort": "high", // Can be "high", "medium", or "low" (OpenAI-style)
    "max_tokens": 2000, // Specific token limit (Anthropic-style)
    // Optional: Default is false. All models support this.
    "exclude": false, // Set to true to exclude reasoning tokens from response
    // Or enable reasoning with the default parameters:
    "enabled": true // Default: inferred from `effort` or `max_tokens`
  }
}