The codebase size will be limited to the LLM context window size. Once the codebase grows larger than the context window, some of the codebase will have to be removed from the context and thus not be known to that LLM instance.

There's also a well documented phenomena [1] where LLMs struggle to recall information in the middle of the context.

[1] https://charlesanthonybrowne.medium.com/how-llms-end-up-igno...