> Don't know, whatever VS Code's bot uses

The reason I ask about what model is I initially dismissed AI generated code because I was not impressed with the models I was trying. I decided if I was going to evaluate it fairly though, I would need to try a paid product. I ended up using Claude Sonnet 4.5, which is much better than the quick-n-cheap models. I still don't use Claude for large stuff, but it's pretty good at one-off scripts and providing advice. Chances are VS Code is using a crappy model by default.

> no idea what those are or why I have to care

For the difference between chat mode and agent mode, chat mode is the online interface where you can ask it questions, but you have to copy the code back and forth. Agent mode is where it's running an interface layer on your computer, so the LLM can view files, run commands, save files, etc. I use Claude in agent mode via Claude Code, though I still check and approve every command it runs. It also won't change any files without your permission by default.

AGENTS.md and CLAUDE.md are pretty much a file that the LLM agent reads every time it starts up. It's where you put your style guide in, and also where you have suggestions to correct things it consistently messes up on. It's not as important at the beginning, but it's helpful for me to have it be consistent about its style (well, as consistent as I can get it). Here's an example from a project I'm currently working on: https://github.com/smj-edison/zicl/blob/main/CLAUDE.md

I know there's lots of other things you can do, like create custom tools, things to run every time, subagents, plan mode, etc. I haven't ever really tried using them, because chances are a lot of them will be obsolete/not useful, and I'd rather get stuff done.

I'm still not convinced they speed up most tasks, but it's been really useful to have it track down memory leaks and silly bugs.