Reasoning Sandwich Pattern

Purpose

A model allocation pattern that wraps implementation actions with stronger-model reasoning phases. The "sandwich" structure ensures complex tasks get proper analysis before and verification after the core action.

Pattern

[Pre-reasoning] → stronger model (opus)
  ├── Analyze requirements
  ├── Identify edge cases
  └── Define success criteria

[Action] → balanced model (sonnet)
  ├── Implement solution
  ├── Generate code/content
  └── Execute plan

[Post-verification] → balanced or lighter model (sonnet/haiku)
  ├── Verify against criteria
  ├── Check for regressions
  └── Validate completeness

Model Allocation Table

Phase	Recommended Model	Rationale
Pre-reasoning (analyze/plan)	opus	Complex architectural reasoning, edge case detection
Pre-reasoning (Opus 4.8)	opus48	Opus 4.8 makes fewer tool calls and reasons more deeply; pre-reasoning phase should include explicit tool batch planning
Action (implement/generate)	sonnet	Optimized for code generation, balanced cost
Post-verification (review/test)	sonnet or haiku	Structural verification, checklist validation

When to Apply

Scenario	Apply Sandwich?	Reason
New feature implementation	Yes	Needs analysis → code → verification
Bug fix with clear root cause	No	Direct action sufficient
Architecture decision	Yes	Heavy pre-reasoning, lighter action
Batch file edits	No	Mechanical action, no reasoning needed
Security-sensitive changes	Yes	Extra verification phase critical

Integration

This pattern is used by:

• structured-dev-cycle — stages map to sandwich phases
• evaluator-optimizer — generator/evaluator model selection guidance
• deep-plan — research (pre) → plan (action) → verify (post)

Anti-patterns

Anti-pattern	Problem	Fix
Opus for everything	Wasteful, slow	Reserve opus for reasoning-heavy phases
Haiku for planning	Insufficient depth	Use opus for complex analysis
Skipping verification	False completion risk	Always include post-verification phase
Forcing frequent tool calls on Opus 4.8	Fights model's natural reasoning-first tendency	Let Opus 4.8 reason; batch tool calls in pre-reasoning

Opus 4.8 Considerations

Opus 4.8 exhibits a distinct behavioral pattern: fewer tool calls with deeper reasoning per call. This affects how the sandwich pattern is applied:

Aspect	Opus 4.6	Opus 4.8
Tool call frequency	Moderate	Lower
Reasoning depth per call	Standard	Deeper
Pre-reasoning benefit	Plan what to check	Plan explicit tool batch — model will under-call if not guided

Pre-reasoning Adjustment for Opus 4.8

When using Opus 4.8 in the pre-reasoning phase:

1. Explicitly enumerate tools needed — Opus 4.8 may skip tool calls it deems unnecessary
2. Batch tool-call plans upfront — structure the action phase with a concrete tool sequence
3. Prefer fewer, richer tool calls — align with the model's natural tendency

Reference: Best practices for using Claude Opus 4.8 with Claude Code