Tested:

tls1.3 - draft 21

./src/curl -I -v --tlsv1.3 https://tls13.akamai.io/

• Trying 2a02:26f0:d8:385::5f37...
• TCP_NODELAY set
• Connected to tls13.akamai.io (2a02:26f0:d8:385::5f37) port 443 (#0)
• successfully set certificate verify locations:
• CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: none
• ALPN, offering http/1.1
• ALPN, server accepted to use http/1.1
• SSL connection using TLSv1.3 / TLS13-AES256-GCM-SHA384

HEAD / HTTP/1.1
Host: tls13.akamai.io
User-Agent: curl/7.59.0-DEV
Accept: /

< HTTP/1.1 200 OK
HTTP/1.1 200 OK

tls1.3 - draft 18

./src/curl -I -v --tlsv1.3 https://h2o.examp1e.net

• Trying 133.242.206.244...
• TCP_NODELAY set
• Connected to h2o.examp1e.net (133.242.206.244) port 443 (#0)
• successfully set certificate verify locations:
• CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: none
• ALPN, offering http/1.1
• ALPN, server accepted to use http/1.1
• SSL connection using TLSv1.3 / TLS13-AES128-GCM-SHA256

HEAD / HTTP/1.1
Host: h2o.examp1e.net
User-Agent: curl/7.59.0-DEV
Accept: /

< HTTP/1.1 200 OK
HTTP/1.1 200 OK