master branch of this repository tracks the master branch of Istio. It's supposed to generate RPM's frequently, on top of the latest and greatest Istio.
A convenient repository for CentOS with those latest builds is available at Fedora COPR.
Other branches, named release-XXX track released versions of Istio, and are not updated frequently as master.
A convenient repository for CentOS with stable builds is available at Fedora COPR.