# Performance Optimization

## Model Selection Strategy

**Haiku** (90% of Sonnet capability, 3x cost savings):
- Lightweight agents with frequent invocation
- Pair programming and code generation
- Worker agents in multi-agent systems

**Sonnet** (Best coding model):
- Main development work
- Orchestrating multi-agent workflows
- Complex coding tasks

**Opus** (Deepest reasoning):
- Complex architectural decisions
- Maximum reasoning requirements
- Research and analysis tasks

## Context Window Management

Avoid last 20% of context window for:
- Large-scale refactoring
- Feature implementation spanning multiple files
- Debugging complex interactions

Lower context sensitivity tasks:
- Single-file edits
- Independent utility creation
- Documentation updates
- Simple bug fixes

## Extended Thinking + Plan Mode

In Claude Code, adaptive reasoning lets the model choose how much to think for each task.
For Fable models, Sonnet 5 and later, and Opus 4.7 and later, use effort to control reasoning
rather than a fixed token budget. Available levels depend on the model.

Control thinking via:
- **Effort**: Use `/effort` in a session, `--effort <level>` at launch, or `CLAUDE_CODE_EFFORT_LEVEL`. Save a per-model level in `modelSettings` in `~/.claude/settings.json`; the older user-level `effortLevel` key does not apply to Opus 5.5 or newer models.
- **Toggle**: Option+T (macOS) / Alt+T (Windows/Linux), or `alwaysThinkingEnabled` in settings. These cannot disable thinking on Opus 5.5, Sonnet 5.5, or Fable models.
- **Fixed budget**: Claude Code ignores positive `MAX_THINKING_TOKENS` values on adaptive reasoning models. On Opus 4.6 or Sonnet 4.6, set `CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING=1` to use a fixed budget with `MAX_THINKING_TOKENS`.
- **Verbose mode**: Ctrl+O to see thinking output

See [Claude Code model configuration](https://code.claude.com/docs/en/model-config#adjust-effort-level)
and [environment variables](https://code.claude.com/docs/en/env-vars) for supported controls.

For complex tasks requiring deep reasoning:
1. Choose a higher supported effort level, such as `/effort high`
2. Enable **Plan Mode** for structured approach
3. Use multiple critique rounds for thorough analysis
4. Use split role sub-agents for diverse perspectives

## Build Troubleshooting

If build fails:
1. Use **build-error-resolver** agent
2. Analyze error messages
3. Fix incrementally
4. Verify after each fix