Unlike the majority of the various archailect empires, the entity/civilization known as the Eternal is, to all appearances, a single being, though with all the power and complexity of a full scale archailect civilization. Certainly in the rare instances of contact between Eternal ISOs and representatives of other civilizations the Eternal entities have all referred to emselves, regardless of the numbers present, as 'I' and behaved as though ey were all extensions of a single mind.
The Eternal derives eir name from eir apparently almost total focus on methods of extending life into the era of Deep Time, long after the end of the era of star formation. The archailect concentrates eir facilities around neutron stars and black holes as well in deep space at the very limits of Terragen expansion above and below the galactic disk. The entity appears to be working on developing forms of existence capable of surviving into the far future of the universe, including computronium structures adapted to survive in close proximity to black holes, long term storage of baryonic matter in close proximity to black holes, and coherent plasma structures designed to exist in deep intergalactic space.
The Eternal seems to be completely indifferent to the concerns of the majority of Terragen civilization. E has completely ignored all attempts at communication or inclusion within the sphere of the other archailect cultures. However, on the rare occasions when other entities have strayed too close to eir operations, e has generally shown a tendency to either warn or remove the intruding beings rather than summarily destroying them. For this reason, the Eternal is more often considered to be, at least in some faint way, aligned with Sephirotic civilization rather then the ahuman polities.
Physical Eschatology - Text by Anders Sandberg in his Transhuman Terminology Branch of science studying how intelligent life could affect and survive in the remote future.