OpenIndiana follows currently a rolling-release model and all the development is focused on Hipster.
The 151a development series which was a direct descendant of the OpenSolaris project and compatible with legacy OpenSolaris installations is now unmaintained.
Hipster
This series is built using the oi-userland with GCC and consists in the effort to modernize OpenIndiana.
Our main goal is to integrate all software delivered with OpenIndiana into oi-userland build system, in place of the former software consolidations.