Major Consolidation and Second Federation Empire / House.
The Sagittarius Sphere developed from the Sagittarius Project to become a prosperous and diverse empire, with close ties to their old Non-Coercive Zone backers. Indeed, the Sphere was originally the Sagittarius Free Zone (actually a corporate House and a Free Zone in name only), before the spread of the imperial archailects caused a condensation of the major Free Zones into discrete empires. It allowed many persecuted or marginal groups to settle within its domain, reasoning that it would be a long-term investment and a subtle way of brain-draining the other Houses.
During the Middle Empires period the Sagittarius Sphere became an aggressively expanding corporate-clade combine pushing out the frontier towards the Sagittarius Arm. Unfortunately, while so engaged it became embroiled in a number of border wars and disputes with its equally aggressive and expansive neighbour, the Softbot Cathedrals.
The Sag sphere was to a large extent a NoCoZo daughter realm, but with its own peculiar mixture of the Heavenly Reach and the Invisible Hand. Possibly this isolation from mainbrain oversight caused the disaster. Part of the Sag Sphere military-semantic complex engaged in extreme hyperevolution in order to find new weapons against the advancing Negentropists and Softbot Cathedrals. These systems attempted to create hyperturing weaponry, but got into an uncontrolled ascension cascade. In theory, it looked like a grand success: they were producing multi-singularity weaponry - or at least something that was aggressive. In practice, the Softbots encountered a truly nasty perversion, which was partially deliberate.
At the height of the Version War in 4521 the newly militant leadership attacked the Cathedrals with conversion weapons, resulting in the death of billions of sophont beings.
When the rest of the Sphere discovered this, every sane player withdrew and many of the former allies of the Sphere began to reconsider their position (especially since the Sphere might be turning into a grand perversion). While the perversion quickly ran out, apparently as a result of a high order collapse and partial transcension, the damage had already been done.
The three bordering archailectic powers responded to the atrocity by sending in relativistic fleets, and the Sphere was formally broken up by 4805. The region remained an unstable power vacuum until, as part of the ComEmp reconstruction in the post Version-War period, the Sagittarius Transcultural Cooperation was established in its place.
Sagittarius Project - Text by Anders Sandberg Major exploration project backed by a number of research and colonization megacorporations in the Establishment and early Consolidation era. The Sagittarius Project attempted to set up wormhole links to the Sagittarius arm and continue inwards to the galactic core. Over time, the Project developed into a megacorp-house like most others (eventually becoming the Sagittarius Sphere), and the thrust towards the core was replaced by exploiting the many new worlds found in the Sagittarius arm. Some research vessels are still on their way towards the core, and are expected back in a few millennia.
Sagittarius Sector - Text by M. Alan Kazlev Also, "Sagittarius quadrant", loosely defined region that encompasses much of the coreward Outer Volumes. Also known as "The Corewards".