Overall Codebase size vs context matter less when you set it up as microservices style architecture from the starts.
I just split it into boundaries that make sense to me. Get the LLM to make a quick cheat sheet about the api and then feed that into adjacent modules. It doesn’t need to know everything about all of it to make changes if you’ve got a grip on big picture and the boundaries are somewhat sane
So "pretty good at picking up existing codebases" so long as the existing codebase is all microservices.
It doesn't have to be micro services, just code that is decoupled properly, so it can search and build its context easily.
Overall Codebase size vs context matter less when you set it up as microservices style architecture from the starts.
It'll be fun if the primary benefit of microservices turns out to be that LLMs can understand the codebase.