(A presentation from Red Hat Summit)
CentOS Stream is a rolling preview of the next minor version of Red Hat Enterprise Linux (RHEL), allowing you to try it out, and contribute changes into the RHEL development process. Carl George gives a brief overview of how that contribution model works.
See also https://youtu.be/UA5QCqwma7Y for a walkthrough of a contribution. See https://centos.org/stream for more information about CentOS Stream