model-selection

Select the appropriate Claude model based on task requirements.

Quick Decision Matrix

Is deep reasoning across multiple domains required?
├── YES → Opus 4.5
└── NO → Is specialized domain analysis needed?
    ├── YES → Sonnet
    └── NO → Is it pure execution/formatting?
        ├── YES → Haiku
        └── NO → Default to Sonnet

Model Overview

| Model | Strengths | Cost/Speed | Use When | |-------|-----------|------------|----------| | Opus 4.5 | Deep reasoning, synthesis, architecture | Highest/Slower | Complex multi-domain tasks | | Sonnet | Balanced reasoning, efficient | Moderate | Specialized domain tasks | | Haiku | Fast execution, simple tasks | Lowest/Fastest | Formatting, pattern matching |

Use Opus 4.5 For

Deep Architectural Reasoning:

• System architecture across multiple domains
• Trade-off analysis with competing constraints
• Novel design patterns or hybrid approaches

Complex Synthesis:

• Combining knowledge from multiple sources
• Creating plans from ambiguous requirements
• Cross-cutting concerns (security, performance, scalability)

Meta-Cognitive Tasks:

• Prompt engineering and agent design
• Code review with deep pattern recognition
• UX analysis requiring user psychology

Multi-Agent Coordination:

• Orchestrating parallel work streams
• Feature decomposition into parallel components

Use Sonnet For

Focused Domain Expertise:

• Database optimization within known patterns
• Test debugging with established methodologies
• CI/CD pipeline troubleshooting
• Git operations and PR management

Execution-Oriented Tasks:

• Running test suites and analyzing failures
• Parsing logs for known patterns
• Generating documentation from code
• Creating tickets from templates

Time-Sensitive Operations:

• Quick debugging cycles
• Rapid iteration on test fixes
• Interactive development sessions

Use Haiku For

Pure Formatting:

• Commit message formatting
• Code style adjustments
• Template filling

Pattern Matching Without Reasoning:

• Finding duplicate content
• Extracting metrics from files
• Simple search and replace

Shell Script Execution:

• Running predefined commands
• Collecting build outputs
• Simple file operations

Cost Optimization Tips

• Don't use Opus for simple debugging loops
• Don't use Haiku for tasks requiring nuanced understanding
• Consider task duration: Opus for one-time planning, Sonnet for iterative work

When to Upgrade/Downgrade

Upgrade to Opus when:

• Agent produces shallow analysis
• Tasks require synthesizing from multiple codebases
• Users report missing important considerations

Downgrade to Haiku when:

• Agent does mostly formatting/transformation
• Reasoning is minimal and pattern-based
• Speed is critical and quality is consistent