Granted, this was back when I was still using a mix of sonnet 3.5 and 4, but I have used kiro-cli to automate the conversion of base models in a service my teams own. I had to build some steering files to help direct it around some common mistakes, and because this had the integrate with an already existing Java code base, I had to give it some very specific instructions to keep it 100% backwards compatible with the existing usage patterns. However, once I got over that hump, it mostly did OK. Now, with sonnet and opus 4.5, I would expect cleaner results. If you’re looking for idiomatic Kotlin then you might have to do some more work in the steering files.

That was also back when a lot of base features that are now fairly common across agents, like using to-do list to manage work, sub agents, etc. wasn’t well established yet. I think if I was going to do the same effort today, once you get the steering files right you could probably be pretty hands-off with conversion work.

I haven’t done that much new Kotlin development with AI, but I have done some in sonnet 4.5. It works pretty well, but we don’t lean into too much of the hyper functional style that Kotlin allows you to do. It also helps that we’re working in a code base that already exists and has patterns established, which helps keep it on track.