How to Switch Claude Models

I regularly switch between Claude models depending on the complexity of my tasks. Sonnet 4 for most daily work, Opus 4 when I need deep reasoning for complex refactoring or architectural decisions. I use Opus for debugging and solving algorithmic time-complexity issues.

Available Models

• Claude 4 Sonnet (claude-sonnet-4-20250514): Latest balanced performance and speed, excellent for most coding tasks, default choice for daily development
• Claude 4 Opus (claude-opus-4-20250514): Maximum capability for complex tasks, best for complex architectural decisions, slower but more thorough responses, higher token usage
• Claude 3.5 Haiku (claude-3-5-haiku-20241022): Fastest and most cost-effective, good for simple repetitive tasks, limited reasoning capabilities

Switching Methods

1. Command Line Flag (Start Session)

Switch models when starting Claude Code:

# Start with Sonnet 4 (default)
claude --model claude-sonnet-4-20250514

# Start with Opus 4
claude --model claude-opus-4-20250514

# Start with Haiku 3.5
claude --model claude-3-5-haiku-20241022

2. Session Command (Mid-Session)

Switch models during an active Claude Code session:

# Switch to Opus for complex reasoning
/model claude-opus-4-20250514

# Switch back to Sonnet for regular tasks
/model claude-sonnet-4-20250514

# Switch to Haiku for simple tasks
/model claude-3-5-haiku-20241022

Model Selection Strategy

I observe distinct patterns in when each model excels:

• Use Sonnet 4 for: Daily coding tasks, bug fixes and debugging, writing tests and documentation, code reviews and explanations, most refactoring work
• Use Opus 4 for: Complex architectural decisions, large-scale refactoring across multiple files, performance optimization analysis, debugging complex interaction patterns, design pattern implementation, UI/UX design and frontend work
• Use Haiku 3.5 for: Repetitive tasks, simple file operations, basic documentation updates

My Strategy

I start with Sonnet 4 for most tasks. Only switch to Opus 4 when encountering problems that require deeper reasoning. Use Haiku 3.5 when running low on usage limits but need quick assistance.

Token Awareness

Switching models mid-session increases token consumption because the new model must process the entire conversation history. Consider starting fresh sessions when changing models for long conversations.