I am getting really good results from claude. We have a 22-year old legacy system. The system is stable, but had issues as all legacy systems do. Claude has been great for modernizing the codebase, updating dependencies, auditing security, and rapidly adding new features. It has worked well with existing code style and patterns. Sometimes it is a little off-track, but overall it is pretty amazing.

When implementing new features or making large refactoring changes; I use the superpowers:brainstorming skill. That has consistent process which has worked really well. I alway review the code before merging, but most of the time there are few issues to correct.

I don't do 95% coverage, but I have increased it from 65% to about +80% and that is sufficient.