So I know I am just joining a crowd of other experiences, but I have to tell someone.
I am a researcher, coding in c for computation research in the 2000s. Some of the c code I used dated from 1993 (not mine), i revised it in the 2000s. It was working but had bugs in it, mostly memory leaks, and other issues. It was good enough and back then, there was not much visual tools for debugging (was under Linux at the time) so it remains as is.
Few years ago, i ported it to Windows, used Visual Studio and all its tools, no luck on the bugs. Again the original c code was not mine, and it was a nightmare to follow the pointers memory assignment the way they were originally coded. There were global variables used in recursive functions, adding free() functions all around did not help.
Lately, I tried to dump the whole project in other AI, and most of them just broke the code. Then I tried Claude Code. 48h later (because I ran out of usage on first day), it was fixed !!! In just few hours, we reviewed the whole code, it was able to trace the pointers correctly, found the missing memory management and WHERE to put them to not break the code. It pointed out some optimizations I did not even ask for, and added some parallelization to top it off.
I do not know if Claude Code writes good code from scratch or not, but if you have to work with code that is not yours - and any programmer who had to knows how painful that can be - this is a leap forward.