Choosing the wrong model can cost five times more.

I use Opus to plan a feature. It’s the senior engineer of the three: finds the gaps in a codebase, knows when to ask questions, maps the feature before a line of code is written.

I use Sonnet to write the code Opus already planned. It’s the mid-level engineer: codes well, without the architectural judgment.

I use Haiku for classification, labeling, yes/no questions. It’s a calculator for nondeterministic values — “is this picture a car?”

Opus plans. Sonnet codes. Haiku answers.