Sphere 878 was a Borg sphere that was in service in the late 24th century. This sphere had a complement of 11,000 drones.

When the sphere was patrolling Grid 091 in 2377, the Borg Queen noticed that the "voice" of one drone aboard Sphere 878 had become silent, meaning it had become separated from the Borg Collective. Fearing the beginning of a resistance from drones affected by Unimatrix Zero, the Queen initiated the sphere's self-destruct mechanism, thus silencing the voices of all 11,000 Borg drones. (VOY: "Unimatrix Zero, Part II")