Complexity Signal

Overview

complexity estimates whether a prompt needs a harder reasoning path or a cheaper easy path. It maps to config/signal/complexity/ and is declared under routing.signals.complexity.

This family is learned: the classifier compares requests against hard and easy examples using embedding similarity, and can optionally use multimodal candidates.

Key Advantages

• Separates reasoning escalation from domain classification.
• Reuses one complexity policy across multiple decisions.
• Supports hard/easy examples that are easy to tune over time.
• Lets simple prompts stay on cheaper models while hard prompts escalate.

What Problem Does It Solve?

Topic alone does not tell you whether a prompt needs strong reasoning. Two questions in the same domain can have very different reasoning depth.

complexity solves that by estimating task difficulty directly from example-driven signal rules.

When to Use

Use complexity when:

• some prompts need stronger reasoning or longer chains of thought
• easy traffic should stay on cheaper models
• you want escalation policies that are independent of domain
• multimodal reasoning requests need different handling from simple prompts

Configuration

Source fragment family: config/signal/complexity/

routing:
  signals:
    complexity:
      - name: needs_reasoning
        threshold: 0.75
        description: Escalate multi-step reasoning or synthesis-heavy prompts.
        hard:
          candidates:
            - solve this step by step
            - compare multiple tradeoffs
            - analyze the root cause
        easy:
          candidates:
            - answer briefly
            - quick summary
            - simple rewrite

Use complexity with representative hard and easy examples so the learned boundary matches your real routing cost profile.