Wyverns are the physical manifestation of draconic id – “bodily needs and wants, emotional impulses and desires, especially aggression and the sexual drive.” They can breed and produce offspring that are wyverns – most wyverns are offspring of draconic dreams.
They are cunning creatures, more intelligent than any beast – but nonetheless they are about as smart as a cave troll. It is unknown whether they understand Auld Wyrmish.
The Lunar Empire maintains a small number of wyverns that are trained to be rode by elite warriors, priests, and rune lords. Young wyverns are captured in the hills of Billiz by local hunters and sold to the Empire for a great price. These warriors serve important generals, powerful nobles, or satraps. They are very rare, and very expensive. At great price, Sor-eel the Short made use of 9 wyvern riders when he tried to capture the Giant’s Cradle at Corflu in 1621.
Do the Lunar Coders own their own wyverns, or are they on loan?
Like a lot of the other cool stuff they get use as part of their duties, the Coders don’t own their own wyverns per se. They are effectively on permanent loan. If one of the coders lost their wyvern, even they might have wait some time to secure a replacement, or not get one at all.