Introduces an opt-in level-based reasoning toggle (low/medium/high) that
each provider translates to its native parameter:
- Anthropic: thinking.budget_tokens (1024/8000/24000), with temperature
forced to default and MaxTokens auto-grown above the budget.
- OpenAI/xAI/Groq via openaicompat: reasoning_effort string, gated by a
new Rules.SupportsReasoning predicate so non-reasoning models don't
receive the parameter. xAI uses Rules.MapReasoningEffort to remap
"medium" to "high" since its API only accepts low|high.
- Google: thinking_config.thinking_budget + include_thoughts:true.
- DeepSeek: SupportsReasoning=false (reasoner is always-on; the
reasoning_content trace was already extracted via openaicompat).
Reasoning content is surfaced as Response.Thinking on Complete and as
StreamEventThinking deltas during streaming. Provider-side: extracted
from Anthropic thinking content blocks, Google's part.Thought=true
parts, and the non-standard reasoning_content field that DeepSeek and
Groq emit (parsed out of raw JSON since openai-go doesn't type it).
Public API:
- llm.ReasoningLevel + ReasoningLow/Medium/High constants
- llm.WithReasoning(level) request option
- Model.WithReasoning(level) for baked-in defaults
- provider.Request.Reasoning, provider.Response.Thinking
- provider.StreamEventThinking
Tests cover Rules-based gating, MapReasoningEffort, reasoning_content
extraction (Complete + Stream), Anthropic budget mapping, and
temperature suppression when thinking is enabled. Existing behavior is
unchanged when Reasoning is the empty string.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
