Caddy serves HTTP/2 by default.
We learned in v1 that almost no one uses the server push functionality of HTTP/2, so it hasn’t been an implementation priority. Besides, configuring it is awkward at best. No one has really come up with a great way to expose push configuration that isn’t tedious. You basically have to map every possible request where you want to push to all the subsequent resources associated with them.
There’s room for innovation here, and that is never an easy or fast process.