Based on a FIDO2 spec I used it to write a reasonably compliant security token implementation that runs on top of Linux USB gadget subsystem (xcept for attestation, because that's completely useless anyway). It also extracted tests from an messy proprietary electron based compliance testsuite that FIDO alliance uses and rewrote them in clean and much more understandable C without a shitton of dependencies that electron mess uses. Without any dependencies but openssl libcrypto, for that matter.

In like 4 hours. (and most of that was me copy pasting things around to feed it reasonable chunks of information, feature by feature)

It also wrote a real-time passive DTLS-SRTP decryptor in C in like 1 hour total based on just the DTLS-SRTP RFC and a sample code of how I write suckless things in C.

I mean people can believe whatever they want. But I believe LLMs can write a reasonably fine C.

I believe that coding LLMs are particularly nice for people who are into C and suckless.

Have you tried asking Claude 4.6 Opus?