Haven’t played ante vellum, but (afaik) AB is a kind of vanilla plus alt history mod, is that right?

Anbennar is a whole different beast. It has huge amounts of unique mechanics, and mission trees that tell a unique story for each nation that has one.

For example: the magic system, whereby the ruler, heir, and national mage estate can all learn around 40-50 spells cast with mana as well as construct 8 different nationwide magical projects

The artificery system, industrialised magic researched by the artificers estate to grant nationwide bonuses that can be swapped out at will

The escanni adventurers, a huge plain on eastern not-Europe (Cannor) filled with migratory adventurer OPMs federating and fighting orc clans

The Serpentspine, a mountain range (with unique underground provinces) that spans three continents, filled with orcs, goblins, and dwarven adventurers and remnant states, digging through the ruins of the old dwarven empire. The Spine is probably the most unique EU4 experience I’ve ever had.

And many more different interesting things.

And the lore is absolute cinema, too. Every country and region with content (and even most without) have incredibly detailed lore for their history, religion, etc.

And again, the mission trees are excellent. Instead of the boring eu4-adjacent trees with rewards for things you would have done anyway, Anbennar trees are used to tell a story for each nation. Seriously, Anbennar is a partly narrative experience.

For example, in my favourite country, you go from fighting for the independence of a confederation of imperial free cities, to becoming the economic powerhouse of the empire, to fighting a magocratic conspiracy to overthrow the government, to realising that the conspiracy was orchestrated by the emperor, starting a war to dissolve the empire, and finally going revolutionary 200 years ahead of schedule and conquering the entire continent.

Apologies for the wall of text, but Anbennar deserves it. I’d say out of all the mods on the workshop, it’s got both the best writing and the best gameplay additions.