Armorer Dreadnaught Option

I see that Dreadnaught is an option for Armorer listed beneath the Level 3: Arcane Armor section of the subclass details, however the option does not appear in the list of armor models. 

Which version of the Artificer class are you using? The Dreadnaught option was added in the 5.5e version of the Artificer class and isn't available in the 5e version.

Is there a separate version of TCoE that has to be bought specifically for 5.5e?

Quote from TheYogiBear77 >>

Is there a separate version of TCoE that has to be bought specifically for 5.5e?

The 5.5e Artificer is included in the book Eberron: Forge of the Artificer. To use the 5.5e version, you would need to either purchase that book or join a campaign where it's being shared.