Model aliases let you pick a model by role rather than memorizing version numbers. opus, sonnet, haiku, and best all map to the current release of that tier.

What it does

You set opus and Claude Code picks the latest Opus model available on your plan. sonnet maps to the latest Sonnet. best picks whichever model is highest-tier for your account. Aliases update automatically when Anthropic releases new versions, so you don't rewrite scripts every release.

When to use it

Config files that should stay valid across model updates.
Quick switching during a session via /model.
Scripts and routines that target a tier, not a specific version.
Teaching examples where you don't want to pin a version.

Gotchas

Aliases change under you when a new model ships. If you need stability, pin a specific version ID.
Some aliases are plan-gated - best on a Pro plan differs from best on Max.
Benchmarks that depend on a specific model should never use aliases.

Official docs: https://code.claude.com/docs/en/model-config.md