Claude Code offers a highly flexible model configuration hierarchy that allows you to balance speed, cost, and reasoning depth across different tasks. You can switch models instantly during an active session using the /model command, specify a model at startup with the --model flag, or set a permanent default in your ~/.claude/settings.json file using the model key. The system supports semantic aliases like sonnet (default for daily coding), haiku (fast and efficient), and opus (high-reasoning for complex architecture), as well as a specialized opusplan mode that intelligently uses Opus for strategic planning before automatically switching to Sonnet for the actual code implementation. Furthermore, you can fine-tune performance on supported models by adjusting the effortLevel (low, medium, or high), which controls how much "thinking time" Claude allocates to solving difficult logic puzzles versus generating rapid responses.
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