Pass --model when launching Claude Code to select which model runs the session — for example claude --model sonnet for everyday coding tasks or claude --model opus when you need deeper reasoning on complex architecture problems.
Sonnet vs Opus: Choosing Based on Task Complexity
Sonnet is faster and cheaper, so defaulting to it for routine work and switching to Opus only when needed is an easy way to cut costs without sacrificing quality where it counts.
Defaulting to Sonnet to Keep Everyday Costs Low
Make Sonnet your baseline model for routine coding, and treat Opus as a deliberate upgrade for architecture decisions, deep debugging, or multi-file refactors that require stronger reasoning.