[mazswojejzony]

We use both Claude and Codex on a fairly large ~10-years old Java project (~1900 Java files, 180K lines of code). Both tools are able to implement changes across several files, refactor the code, add unit tests for the modified areas.

Sometime the result is not great, sometimes it requires manual updates, sometimes it just goes into a wrong direction and we just discard the proposal. The good thing is you can initiate such a large change, go get a coffee, and when you're back you can take a look at the changes.

Anyway, overall those tools are pretty useful already.