Version 6.4.0 is available upstream. Please consider updating!
It seems that version 6.4.0 is available upstream, while the latest version in the Gentoo tree is 6.3.1. You think this warning is false? Read more about it here.
Puma is a simple, fast, threaded, and highly concurrent HTTP 1.1
server for Ruby/Rack applications. Puma is intended for use in
both development and production environments. In order to get the
best throughput, it is highly recommended that you use a Ruby
implementation with real threads like Rubinius or JRuby.