Is the Armorer artificer's Arcane Armor magical?

Question

Is an Armorer artificer's Arcane Armor magical?

As far as I've seen, the rules do not clearly state that the armor becomes a magical object. In addition, an argument can be made that the rules indicate that an artificer can infuse Arcane Armor even though an artificer cannot infuse magic items.

This is further modified by the Armor Modifications feature at 9th level, which allows different components of the armor to be infused separately. Though this might be a case of the specific overriding the general, so it may be the case that the base Arcane Armor is magical.

However, the description also includes the text "The artificer bonds with this armor, becoming one with it even as they experiment with it and refine its magical capabilities." If this is the key piece of information, then this might be a question about whether these "magical capabilities" are an ongoing magical effect, or reflect the idea that the armor has the potential to be enchanted (infused) and thus become magical.

The criteria for being magical are:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

The uncertainty is in the first and last criteria. Given the name, "Arcane Armor" and the sentence indicating that it has "magical capabilities". Does this satisfy either the "is magic item" or "description says it is magical" criteria?

This is relevant for adjudicating actions like Detect Magic or others where the presence/absence of magic effects/items are relevant.

Answer 1

An Artificer's Arcane Armor is meant to be infused.

The Armorer subclass even has a feature to enhance it. Note that the feature does not call out infusing your arcane armor in this case as an exception to a general rule where the armor is not infusable.

At 9th level, you learn how to use your artificer infusions to specially modify your Arcane Armor. That armor now counts as separate items for the purposes of your Infuse Items feature: armor (the chest piece), boots, helmet, and the armor's special weapon. Each of those items can bear one of your infusions, and the infusions transfer over if you change your armor's model with the Armor Model feature. In addition, the maximum number of items you can infuse at once increases by 2, but those extra items must be part of your Arcane Armor.

So no, designating a piece of armor does not make it magical, the wording carefully avoids calling it magical, likely specifically to allow an infused armor.

Answer 2

Under a strict reading of the rules, the Arcane Armor being magic depends on the Artificer level.

As you pointed out, the basic definition of Arcane Armor does not specify if such Armor is magic or not. But you have to choose between the Guardian or the Infiltrator model for the armor. In the former case, the description says (emphasis mine)

A creature hit by the gauntlet has disadvantage on attack rolls against targets other than you until the start of your next turn, as the armor magically emits a distracting pulse when the creature attacks someone else.

Hence, in case of using the Guardian model, the description of Arcane Armor specifies the magical nature of the armor. The Infiltrator, on the other hand, does not present any reference to a magical nature.

Under the level progression, at level 9 the Artificer can infuse some part of the armor, making such parts magic items.

At level 15th both models provide evidence that the Arcane Armor is magical:

Guardian. When a Huge or smaller creature you can see ends its turn within 30 feet of you, you can use your reaction to magically force it to make a Strength saving throw against your spell save DC.

Infiltrator. Any creature that takes lightning damage from your Lightning Launcher glimmers with magical light until the start of your next turn.

In conclusion, before the 9th level the Arcane Armor is magical (by description, fulfilling hence the last criterium of the SAC) when the Guardian model is employed, at 9th level some parts of the Armor can become magical thanks to the Infuse Item feature of the class (they become magic items), and finally at 15th level both models are magical (again by description).

Answer 3

Some of the Armor's features are magical

The context of the criteria is key in this case:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

So what game feature are we applying these criteria to exactly? Although the armor we choose to apply our class features to is temporarily called the Arcane Armor, it is not a single game feature, so we can't apply the criteria to it as a whole. Instead, we need to look at each game feature separately: the armor, Arcane Armor, Armor Model, Armor Modifications, and Perfected Armor. Each of can be magical or not, independently of the rest.

The Armor

Here I'm referring to the item itself, distinct from the class features. Whether the armor is magical boils down to whether it is a magic item, which should be easy to figure out from item's description.

Arcane Armor

It's not a magic item, nor spell, because it's a class feature. It doesn't create the effect of a spell, it's not a spell attack, nor is it fueled by spellslots. This holds true for the other class features too, so I won't repeat myself later.
The description doesn't say that it is magical either, so the Arcane Armor feature isn't magical.

Armor Model

Its description states:

Guardian. You design your armor to be in the front line of conflict. It has the following features:
Thunder Gauntlets. [...] as the armor magically emits a distracting pulse when the creature attacks someone else.

So this game feature is definitely magical, but in this case it is still unclear what the game feature in question is: the Armor Model feature, the Guardian model, or the Thunder Gauntlets feature?
The guidelines we are given are too vague to give a definitive answer, but I would be inclined to rule that the entire Armor Model feature is magical, because if I don't then the Thunder Gauntlets would bypass resistances to damage from non-magical weapons, while the Lightning Launcher wouldn't, and I simply dislike that discrepancy.

Armor Modifications

The description doesn't say that Armor Modifications is magical, so it isn't, but the Arcane Infusions it grants most definitely are.

Perfected Armor

Its description states:

Infiltrator. Any creature that takes lightning damage from your Lightning Launcher glimmers with magical light until the start of your next turn.

So this game feature is definitely magical. Here too there is ambiguity whether the game feature in question is the Armor Model feature or just the benefits granted to the Infiltrator model, but for consistency's sake I'd rule the former.

In Practice

So, someone casts detect magic in the presence of an Armorer, what is sensed?
Detect magic won't sense magical class features like Armor Model and Perfected Armor any better than it would sense the Spellcasting feature. However, if the armor is a magic item, that is sensed as normal, as are any magic items created via Magical Infusions.

Then, somebody casts anti-magic field, how is the Armorer impacted?
The Armor Model and Perfected Armor features are magical and fall in the spell's "Targetted Effects" section: Thunder Gauntlets targets an enemy, Powered Steps targets the Armorer, and so on for the other abilities in those two features.
The Arcane Armor and Armor Modifications features aren't magical, though the later becomes functionally useless because...
All the magic items become mundane per the spell's "Magic Items" section, including the ones created via Magical Infusions and the armor if it was a magic item.