In the Imperial Armour Index Xenos, the Canoptek Acanthrites are listed with a Voidblade, but it's missing the regular text about granting an extra attack.
I saw there was an old thread from 2017 (
www.dakkadakka.com/dakkaforum/posts/list/737375.page#9570687) lying around, but was adviced by the forum itself to post a new question, as the thread was very old.
The original question was the same, and the reply was that there was an errata that added the ability text, but strictly speaking, the errata was for the regular Index Xenos 1, where indeed it made sense to add the ability text.
Since then, the official update for Imperial Armour Index Xenos has come to version 1.3 (
www.warhammer-community.com/faqs/?orderby=title&order=asc#items-warhammer-40000), and there's still no mention of either the Acanthrites or the Voidblade.
I'm planning to play these creatures for the first time now, and I'm wondering about how to interpret this. As the Voidblade is their only melee weapon option, you'd think that perhaps the attack profile reflected any special characteristics of the weapon already? Why bother writing 3, when you'd always have 4 in any case? I must admit that I'm not familiar enough with all other units to know if this is the case for any other.
The other units that have the option of taking the Voidblade (Catacomb Command Barge, Overlord, Lord, Destroyer Lord and Triarch Praetorians) all have other melee weapon options. Then it makes sense to have a base number of attacks and then up it by one when using the Voidblade.
So, even though I'd like the 'thrites to have 4 attacks, I'm wondering if they only have 3 in this case?