Antimatter Reactor

Violently converting antimatter and matter into energy, these reactors have higher yields than fusion alternatives but can have undesirable explosive properties if their fuel storage is damaged.

Utility

Less sophisticated interstellar nations utilize antimatter reactors as their primary power source for large-scale constructions such as ships and outposts. Being more powerful than fusion reactors, the risks associated with storing and handling extremely volatile antimatter are acceptable. Antimatter warheads can also be mounted on torpedoes or electromagnetic accelerator rounds, with similar caveats for safety and secondary explosions.
More advanced civilizations tend to replace antimatter reactors with singularity cores, although (like with the Sagittari) antimatter may continue to be used in backup applications.

Access & Availability

Although less common as fusion reactors, antimatter reactors are not conceptually complex or difficult to build for an interstellar empire. Minor spacefaring powers such as certain weaker Kri'tak clans are forced to use these instead of singularity cores.
The Sagittari Union also utilizes antimatter/matter reactors in limited quantities.