The Optica Giganta were the last vehicles ever constructed by the Elder Reminders species before their ascension.
An advanced species that barely survived their home system's supernova, the Elder Reminders were obsessed with high-energy natural events and how civilizations could survive them. They spent all their resources causing, observing, and mapping events such as supernova and Duowave Pulse warp events, as well as all species affected by them.
Their civilization began to fall apart when they appeared to discover an edge case in the Theory of Physical Undecidability which could allow them to view their lost home... or perhaps even avert the disaster.
Efforts to determine whether this was possible or not were met with endless misadventure, culminating in several more supernova events and the only time a Kandar Lithoglyph was lost.
Finally, the Elder Reminders decided to embark on a grand construction project.
In theory, the fluctuations left behind after high-energy events could be used to reconstruct not just the event, but the exact state of the system before the event, down to the atomic scale. In practice, it would take the computing power of several solar systems and a sensor kit the circumference of a small moon.
The Optica Giganta were space ships the size of a small moon, ringed with sensors and stuffed full of computers.
With nearly all the Elder Reminders aboard Optica Giganta ships, the species effectively vanished from interstellar civilization and spent their last centuries traveling the universe, from star to star, occasionally blowing one up to test their systems. The prototypes seen at locations such as the X-2814 Supernova Event and the Prow Flare were already staggering feats of engineering, but as they were refined, they faded out of existence.
Nobody's quite sure what happened to the Optica Giganta and the Elder Reminders. Are they still wandering, but invisible? Did they return to their sacred, long-lost homeworld? Did they reconstruct it around some faraway star, and are now living there?
The intergalactic community just rubber-stamped "ascended" on their claimed star systems, and put them up for auction.