The latest version of Nagios in portage is 4.4.6, but 5.8.1 is available on the nagios.org web site.
I'm not familiar with Nagios but I assume you're looking at Nagios XI, which is a commercial extension to Nagios Core that I do not believe can be offered here. Gentoo is packaging said nagios-core (as part of the net-analyzer/nagios metapackage) and 4.4.6 is still latest. https://www.nagios.org/projects/nagios-core/history/4x/ I'll close this, but if you believe I'm mistaken I'll re-assign to the Nagios maintainers.
(In reply to Ionen Wolkens from comment #1) > I'm not familiar with Nagios but I assume you're looking at Nagios XI, which > is a commercial extension to Nagios Core that I do not believe can be > offered here. > > Gentoo is packaging said nagios-core (as part of the net-analyzer/nagios > metapackage) and 4.4.6 is still latest. > > https://www.nagios.org/projects/nagios-core/history/4x/ > > I'll close this, but if you believe I'm mistaken I'll re-assign to the > Nagios maintainers. Correct, the latest nagios core version is 4.4.6 - https://github.com/NagiosEnterprises/nagioscore/releases