High Humans

While the abhorrent history of the Xylian Dominion has ruined image of the genmaturgy among the inhabitants of Karadia, not all of its applications were rendered equally repugnant in the eyes of the public. As a result, while the additive genetic modifications were an absolutely horrifying concept (resulting in Warforged supersoldiers being achieved through dual means of surgeries and alchemical enhancements), the reductive or transgenic modifications were slightly less controversial.
The results of the application of those means to the imperial population as a whole were great. During the Second Era, the imperial government launched mass-scale project for maping the imperial genetics. And a few decades later yet another project, this time tasked with artificial spread of beneficial genes throughout the entire imperial population, with simultaneous erasure of majority of genes that were found to be harmful.
The Second Empire hasn't created any new genes, only perpetuated those already in-existence - it also made the modification mandatory to all of its human citizens, making no distinction between nobles, commoners and slaves. The idea of creating a genetically divergent caste of citizens - for whatever reason - was one of the things that the Dominion rendered repugnant. Although that was achievable only thanks to the baseline Mankind' genetic moldability, meaning that species previously modified (like the Elves) couldn't go through the process, and in case of human subspecies like Beastkin the modifications didn't touch their supernatural half.
The process ended with an astounding success. However, it lasted only for a few decades - as that's when the Twilight War started. The plan for a follow-up genmaturgic process - that one would 'fix' defficiencies of the previously-divergent species, such as many subspecies of the elves - were naturally scrapped, as almost all alchemists with necessary knowledge died during the first minutes of the War.
As a result, the High Human genetic template has began long process of decline. Five hundred years is enough of a time for random mutations to cause growing number of divergences. As a result, even among the highest nobility (which maintains a monopol on the access to the few remaining genmaturgists capable of 'fixing' the newly emerging flaws), there are more and more divergencies. This is made to occur even faster through for example accidents with aether refining (often resulting in spread of mutagenic materials) or thankfully rare cases of interbreeding with the non-enhanced humans (primarily those from outside of the Karadia).

Basic Information

Anatomy

High Humans are, to be honest, humans - but better. The process to created them isolated the list of beneficial, neutral and harmful genes in the entire imperial human population, and got rid of the last category, while making the first type to a degree mandatory.
This has notably unified the morphology of the imperial population, making it more likely to be tall, reasonably muscular (men more than women, although they are notably above 'baseline' human average as well), not obese, and good-looking.
The same changes made the imperials much more resistant to genetic defficiencies (that were practically purged from the Grand EMpire, although have recently began to creep back in), although there are still (even if rare) birth defects.
It has to be said that all the changes aren't guaranteed to occur, both due to epigenetics and simple fact that the goal of the project wasn't to make everyone in the Empire identical. People from different ethnic groups within the Empire have maintained their originality (including those from the Descent, who were given bodies 'normal' for the empire, so of this subspecies).
There are also external factors (starting from something as basic the amount of nutrition received while growing up) that influence the outcome. There are fat and weak imperials, but the chance of an imperial turning that way is significantly reduced when compared to baseline human of similar upbringing).

Biological Traits

The High Humans as a subspecies were created by people with certain views on the world - and those views are at least slightly reflected in the general aesthetics of their creations. One of the most significant result is a slightly sharpened gender dimorphism among the imperials. It is best described as 'males are to be tough and strong while females should be agile and dexterous'.
This is a tendency rather than strict rule, made even worse by the passage of time and the deterioration of the high human genetic template. What's more, both genders receive updates on both sides. Just because female high human are supposed to be dexterous rather than strong doesn't mean that their strength wasn't upgraded above regular human male's average.
Hilariously enough, high humans are also universally taller than regular humans. High human males are taller than females (2,1m to 1.9m), but both genders are universally taller than their baseline human peers. In fact, high human females are taller than regular human males, at least on average.
The gender dimorphism is purely physical. No changes were made to intelligence and emotions. Talents for magic weren't touch either, and are roughly identical for both genders.

Genetics and Reproduction

They are essentially humans with purified genome - or at least that's what they were when they were created. During the past five centuries minuscule damages has began accumulating in their genes. Many are still identical with the 'original' result of the project, but others are slowly degrading back to the baseline humans. The process is far from happening fully, and in fact is extremely unlikely to be concluded within reasonable timespan - according to estimation of imperial genmaturgists, it will take several millenia for the imperials to become genetically indistinguishable from baseline humans again.
Other than that, there are no differences on the level of genetics - and in reproduction - from the baselines. They are, by all intents and purposes, humans. They can interbred with the species that the baseline humans can.

Additional Information

Perception and Sensory Capabilities

The imperials have as a rule good eyesight, hearing, smell, taste and touch - however they are good per human norm. In short, imperials have them on the above average level for classic unaugmented human, but there are such people who surpass imperial average. This is getting more and more common as time passes, as random genetic defficiencies slowly find their way into the imperial population.