It's one HTTP request per call, but requests usually flow over a persistent connection in HTTP 1.1 - it's certainly not re-opening a connection for every reques

It's one HTTP request per call, but requests usually flow over a persistent connection in HTTP 1.1 - it's certainly not re-opening a connection for every request. TCP reconnection and stuff like that is at a lower level than Twirp. When you make a client of a Twirp service, the constructor accepts a http.Client which it'll use to send the requests. http.Client has a "Transport" field which is responsible for opening connections, that sort of thing. The Go standard library's defaults are pretty good, but you can tune it as you like.