A form of distributed intelligence; an intelligent being with parts spread across an entire galaxy. If not linked by wormholes, the internal communication lags would be on the order of tens of thousands years, making the top level very slow (but subminds could be much faster). The parts could be jupiter brains or other intelligent superobjects. While some Keterists and MPAists have suggested that the technosphere is evolving towards a state of a single Galaxy Brain, and ultimately a single Universe Brain, there is no evidence that this is so, as SI:<1 sentients are just as common, proportionally speaking, now as they were during the early Empires period.
Some commentators believe that some, or many, distant galaxies are already converted into galaxy brains by xenosphont civilisations far more advanced even than the Orion Arm Civilisation; but little evidence of this conjecture is yet available.
It may be the case that Galaxy Brains are not necessary, since computation using artificially constructed basement universes might offer a more efficient option.