I know it isn’t your question exactly, and you probably know this, but the models for coding assist tools are generally fine tunes of models for coding specific purposes. Example: in OpenAI codex they use GPT-5-codex
Like, how feasible is it for a mid-size corporation to use a technique like LoRA, mentioned by GP, to "teach" (say, for example) Kimi K2 about a large C++ codebase so that individual engineers don't need to learn the black art of "context engineering" and can just ask it questions.
LoRa doesn't overwrite weights.