What models are you using that you feel comfortable trusting it to understand and operate on 10-20k LOC?
Using the latest and greatest from OpenAI, I've seen output become unreliable with as little as ~300 LOC on a pretty simple personal project. It will drop features as new ones are added, make obvious mistakes, refuse to follow instructions no matter how many different ways I try to tell it to fix a bug, etc.
Tried taking those 300 LOC (generated by o3-mini-high) to cursor and didn't fare much better with the variety of models it offers.
I haven't tried OpenAI's APIs yet - I think I read that they accommodate quite a bit more context than the web interface.
I do find OpenAI's web-based offerings extremely useful for generating short 50-200 LOC support scripts, generating boilerplate, creating short single-purpose functions, etc.
Anything beyond this just hasn't worked all that well for me. Maybe I just need better or different tools though?