See the mediawiki page.
D7 is supported for production thru its EOL in November 2021.
D8 is supported for development of the dual version feature, to support clients that may have committed to it on a custom consult basis, and to track development of D9.
D9 is scheduled for a forced release in early 2020 due to Symfony mandate at which time it will be reevaluated for production.
Login to D7 domain logs in to the extension for developer role, the login here is for operator role.