Maybe, for some projects, instead of generating code with it, it would be useful to generate a plan and the loop(tests/formal verification),because those take much less tokens than a full project, and than use the loop using the older models ?

Yes, I've been using Opus to write a plan and fanout sonnet subagents to implement it. Cheaper and faster

This is the goal behind Devin Fusion, pretty good results so far I think.

https://cognition.com/blog/devin-fusion

Has anyone experimented with Batch Processing? According to https://claude.com/pricing#api using Batch processing cuts the price 50%. So I wonder if any of the harnesses like OpenCode/Pi or similar could be made to use that for planning or similar.

this is the idea of opusplan https://code.claude.com/docs/en/model-config#opusplan-model-...

Isn't that the kind thing its best at as well? Art least comparatively with other models. The more agentic stuff. Planning, tool orchestration, etc.

I think that's the idea, I saw some outrage on reddit about Fable using Opus to do code writing, another comment said exactly my reaction, why do you want to pay double for tool calling when Opus is just fine for the task?

But wouldn't that still result in higher token usage to scan the code base and figure out the changes and generate the plan? In my experience sometimes Opus launchs a Haiku sub-agent to explore the code base, but it's not gaurenteed.

Yes, I do this all the time in Cline. It supports automatic model change when switching from Plan mode to Act (implementation) mode. Opus for planning and Sonnet for implementation. It works great.