The Architects (name given by Alterra) were an advanced, ancient space-faring race who arrived on Planet 4546B 1000 years prior to the events of Subnautica in search of a solution to cure the infamous Kharaa bacterium. The Architects are almost 100% mystery, however a Data Bank entry claims that a ninety-six year old individual is considered to be very young, and the same individual was later described at the age of seven-hundred and eight. Architects are/were (presumably) much larger creatures than humans due to the sheer size of the rooms in their bases, and most objects within. It is probably that the Architects were bio mechanical entities.
The Architects were clearly an extremely advanced race; Much more than humans. They had the capability to travel across galaxies, implying incredibly advanced spacecraft and propulsion technologies. They had the technology to create robotic drones that could survive in severely heated areas, teleporters and a weapon capable of destroying huge ships (such as the Aurora). They also had the capability to produce bio mechanical lifeforms, presumably through advanced gene engineering. Architects technology requires "keys" or "artifacts" to open certain force-field gateways via an Artifact Terminal.
The Architects civilization was destroyed by the Kharaa, a bacterium that spread quickly to many Architects worlds and causes sickness and death. Billions of Architects died, although seemed to have the technology to store their consciousness digitally before death. 
Planet 4546B was designated as a Disease Research Facility planet. The Kharaa was tested on local species hoping one would show a resistance to the bacteria.
Extreme safeguards were put in place to prevent the spread of the Kharaa off world if it ever leaked into the local ecosystem. The Quarantine Enforcement Platform (QEP) is a colossal Architects super weapon designed to destroy any unauthorized spacecraft from entering or leaving Planet 4546B's atmosphere. Architects also created a synthetic race, known as "Warpers" or Self-Warping "Quarantine Enforcer Units". These self-teleporting bio-mechanical creatures were advanced enough to track and kill all fauna in advanced stages of Kharaa infection.
Other structures on 4546B include the Thermal Power Generator (PTPG), A base situated in the Active Lava Zone, which draws power from the nearby lava to power Architects structures. And the Primary Containment Facility (PCF), an aquarium that contains the Sea Emperor, a creature which is immune to the Kharaa.