@louis No, there are 64 threads handling connections, i.e. reading requests and writing responses. However these read and write operations are blocking, meaning that they only return once data have been read/written. Without buffering, if a client opens 64 connections and does not send anything, the server will lose the ability to process requests.
With a buffering reverse proxy, e.g. NGINX, the proxy manages connections in a non-blocking way (usually with epoll or kueue), without requiring one thread per connection, and accumulates requests until they are complete, then only forward them to the real server. No risk of blocking. Of course in theory I could write the HTTP server in a non-blocking way in Common Lisp, but then we're back to the lack of green threads, callback hell, etc.