Can AI coding assistants work on large existing codebases?
Yes, and that is where they earn the most, but the limitation is context. They can read the code and cannot read undocumented intent: the architectural rules that live in people's heads. On a large codebase that gap is where the expensive mistakes come from.
From Cursor, Copilot, Claude Code: assistants compared, updated 9 August 2026. That article is where the reasoning behind this answer is set out, including what it does not cover.