  We review the current status of the minimal non-supersymmetric SO(10) grand
unified theory and perform a detailed next-to-leading-order analysis of the
gauge unification and proton lifetime constraints on the part of its parameter
space supporting a ZeV-scale color sextet scalar. This, together with a
TeV-scale color octet studied in detail in a preceding work, represents one of
the two minimally fine-tuned settings compatible with all the relevant
consistency and phenomenology limits. Both these scenarios can be extensively
tested at the future megaton-scale proton-decay facilities. On top of that, the
light octet solution can be accessible in the TeV-scale collider searches.
