the largest single caste of humans are near-baselines, who have relatively few admixtures from genetically engineered persons and who are mostly humans. the most _human-appearing_ people are the highborn castes, who have had a selection of more or less uniformly positive traits applied.
then there are labor castes, who are engineered (mostly) to be large, dumb, and compliant. there are warbred castes, who are very dangerous in individual combat but have very short lifespans. there are semi-sentients like Mutterers and the Sickly. then there are the Technical Castes.
immediately before the Interdict came down, there was a civil war started by the Technical Castes over the testament of the Eighth Oracle. the Emperor released a plague which sterilized them, and the Creche Bureau created the Mutterers to replace them.. this is the cause of a lot of problems.
because while Mutterers are excellent engineers, they cannot really be told what to do in any meaningful way, meaning that there is essentially no standardization of high-tech equipment and machine tools, and virtually everything is subjected to repair and modification.
so while, e.g., industrial-age firearms are pretty common, the widely variable bores of indiviudal weapons mean that ammunition is all handmade. that and the fact that guilds control virtually all manufacturing mean that mass production is more or less a lost social technology.
so what was the long-term plan of the guys who genocided their engineers and replaced them with guys who don't take orders? because that doesn't seem like a great way to keep having a technological civilization
the Emperor appears to have wanted everyone to follow him into a black hole relatively shortly afterwards, but for reasons related to time dilation that has not quite worked out.