The author very much did try to do that, doing requests with async APIs is often the most performant way to do them because under the hood they use IO async pri

The author very much did try to do that, doing requests with async APIs is often the most performant way to do them because under the hood they use IO async primitives like epoll/kqueue/iocp depending on the environment they run on. If you check the code in the article, there is an innocent looking call to decode the response as JSON; that's most likely where the CPU time is going, most JSON decoders are just not very fast. I remember back in the day having to write my own decoder for a JSON API because I was getting capped on around 250req/s on a windows machine (using c# and iocp which is pretty fast). I think I almost doubled performance by taking some decoding shortcuts when the JSON structure was known ahead of time. TL;DR: network I/O is fast, json is a really slow format to parse.