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# Claude 4.6 Migration Guide

## What's New

See Anthropic's [What's new in Claude 4.6](https://platform.claude.com/docs/en/about-claude/models/whats-new-claude-4-6) for a full overview of new features.

Claude 4.6 Opus and 4.6 Sonnet introduce two major changes to reasoning:

1. **Adaptive Thinking** — Claude decides how much to think based on task complexity, replacing budget-based extended thinking
2. **Max Effort Level** — A new `'max'` effort level above `'high'` (Opus 4.6 and Sonnet 4.6 only)

## Adaptive Thinking

For Claude 4.6 Opus and 4.6 Sonnet, OpenRouter now uses adaptive thinking (`thinking.type: 'adaptive'`) by default instead of budget-based thinking (`thinking.type: 'enabled'` with `budget_tokens`).

### How it works

* When you enable reasoning without specifying `reasoning.max_tokens`, Claude 4.6 Opus and 4.6 Sonnet use adaptive thinking
* Claude automatically determines the appropriate amount of reasoning based on task complexity
* You don't need to estimate or tune token budgets

### When budget-based thinking is still used

* If you explicitly set `reasoning.max_tokens`, budget-based thinking is used
* If you pass the raw Anthropic `thinking` parameter directly

```json
// Adaptive thinking (recommended for 4.6)
{
  "model": "anthropic/claude-4.6-opus",  // or "anthropic/claude-4.6-sonnet"
  "reasoning": { "enabled": true }
}
```

```json
// Budget-based thinking (still supported)
{
  "model": "anthropic/claude-4.6-opus",  // or "anthropic/claude-4.6-sonnet"
  "reasoning": { "enabled": true, "max_tokens": 10000 }
}
```

## Max Effort Level

A new `'max'` effort level is available for Claude 4.6 Opus and 4.6 Sonnet via the `verbosity` parameter. See Anthropic's [effort documentation](https://platform.claude.com/docs/en/build-with-claude/effort) for details on how effort controls response thoroughness and token usage.

```json
{
  "model": "anthropic/claude-4.6-opus",  // or "anthropic/claude-4.6-sonnet"
  "verbosity": "max"
}
```

`'max'` is only supported on Claude 4.6 Opus and 4.6 Sonnet. For other models, it automatically falls back to `'high'`.

## Verbosity vs Reasoning Effort

These are separate parameters:

| Parameter          | Controls                                 | 4.6 Behavior                             |
| ------------------ | ---------------------------------------- | ---------------------------------------- |
| `verbosity`        | Response detail (`output_config.effort`) | Works normally, supports `'max'`         |
| `reasoning.effort` | Thinking token budget                    | Ignored (adaptive thinking used instead) |

```json
// verbosity works - controls response detail
{ "model": "anthropic/claude-4.6-opus", "verbosity": "max" }  // also works with anthropic/claude-4.6-sonnet
```

```json
// reasoning.effort ignored - still uses adaptive
{ "model": "anthropic/claude-4.6-opus", "reasoning": { "enabled": true, "effort": "low" } }  // also applies to anthropic/claude-4.6-sonnet
```

## Breaking Changes

None. Existing requests continue to work:

* Budget-based thinking still works when `reasoning.max_tokens` is set
* `reasoning.effort` values (low, medium, high) are still supported for older models, but will be ignored for Opus 4.6 and Sonnet 4.6. Use `reasoning.max_tokens` to control Anthropic's `thinking.budget_tokens`, and `verbosity` to control Anthropic's `output_config.effort`.
* Older models (4.5 Opus, 3.7 Sonnet, etc.) behave exactly as before

| Feature                | Opus 4.5             | Opus 4.6 / Sonnet 4.6 |
| ---------------------- | -------------------- | --------------------- |
| Default Thinking Mode  | Budget-based         | Adaptive              |
| `reasoning.max_tokens` | Budget-based         | Budget-based          |
| `verbosity: 'max'`     | Falls back to `high` | Supported             |