10k-15k+ code line projects possible?

Is there any programming technique to use with Claude to help it understand projects that are larger in size that around 10k-15k lines of code?

I always end up letting Gemini give me the file structure, classes and functions with their args because of it's 2 million token context window, but this way Claude has a hard time avoiding mistakes because of incomplete understanding.

I then try to provide the main function and relevant files or snippets, but I always get to a point where it feels like the coding process is getting so slow that I could just do it by hand at this point.

I'm already splitting up larger files with Claude, letting it create a python script to create the files and fill them with their code, but often it gets confused on how to correctly replace the older large file with the new smaller files, which are often inside a new folder. Sometimes it works, sometimes it doesn't and in the end it might end up even more confusing because suboptimal file and class naming.