The easy decision is to just go with the biggest SOTA model you can afford.

But this overlooks the other critical part of getting the most out of these things: the harness. I run an autonomous plan/design/code/build/test pipeline with agents using my own orchestrator. Different models are better at different stages, and I use LLMs to judge the output between them. Not everything needs Opus 4.8.

The harness provides both the scaffolding to get the right things into the model, and the right things out. But it also lets you dictate which model does which work.

It's the pipeline, not the model, that gets you quality at a given token budget.