Quarkus httpClient (quarkus-rest-client) should be able to works over http/2 as the server-side does. Otherwise, if we use quarkus-rest-client for example to exchange data between microservices, then the server(even if is able to talk on Http/2) will talk on the same protocol as the client libraries (Http1.1).

Conclusion from Clement from 2023-12-20: The reactive REST client supports HTTP/2 so, I'm considering this issue as completed. The reactive rest client is our recommended client.