Seven years ago we ditched HTTP Pipelining support in #curl.
https://daniel.haxx.se/blog/2019/04/06/curl-says-bye-bye-to-pipelining/

curl says bye bye to pipelining
HTTP/1.1 Pipelining is the protocol feature where the client sends off a second HTTP/1.1 request already before the answer to the previous request has arrived (completely) from the server. It is defined in the original HTTP/1.1 spec and is a way to avoid waiting times. To reduce latency. HTTP/1.1 Pipelining was badly supported by curl … Continue reading curl says bye bye to pipelining →