All these conversations seem like they are missing talking about planning vs execution. I want the best possible frontier model to plan out my changes. I also have a 2nd agent that is a frontier model check the plan. Then at that point the implementation can be done by a lesser and possibly local model. The frontier model can still do a final code review on the implementation of the changes.

Claude code supports this by setting the model to "opusplan"- it will automatically use Opus for planning and sonnet for implementation. This was completely necessary with the fable release. I was able to do this with fable and it was necessary to avoid getting quickly rate limited. In settings.json:

"env": { "ANTHROPIC_DEFAULT_OPUS_MODEL": "claude-fable-5" },

Obviously have that set to "claude-opus-4-8" now.