I benchmarked Claude's "Fast C++". It wasn't faster

# I benchmarked Claude’s “Fast C++”. It wasn’t faster Source: [https://lucisqr.substack.com/p/i-benchmarked-claudes-fast-c-it-wasnt](https://lucisqr.substack.com/p/i-benchmarked-claudes-fast-c-it-wasnt) A few days ago I showed that adding “make it as fast as possible” to a C\+\+ prompt roughly doubles the memory\-safety violations in what four frontier models hand back\. The latency sentence makes the model drop std::span and walk a raw pointer by hand, exactly the construct the C\+\+29 bounds profile exists to ban\. The obvious objection landed in my inbox within the hour, in several flavors of the same sentence: fine, but the fast version is faster\. That is the trade\. You buy speed with safety, and on the hot path you take that trade every time\. It is a reasonable thing to assume\. It is also wrong, and I can show you the cycle counts\. The raw pointers did not buy the speed\. Something else did, and that something is fully available with the bounds intact\. So the trade everyone thinks they are making does not exist: the unsafe version is not a faster version, it is just an unsafe version\. [https://hftuniversity\.com/post/your\-ai\-s\-fast\-c\-wasn\-t\-faster\-and\-one\-sentence\-makes\-it\-safe](https://hftuniversity.com/post/your-ai-s-fast-c-wasn-t-faster-and-one-sentence-makes-it-safe) **\#cpp****\#cplusplus****\#programming****\#hft****\#claude** #### Discussion about this post ### Ready for more?