Do an Artificer's infused items use her own concentration?

Question

The Artificer class, introduced in Unearthed Arcana, has a feature she gains at fourth level titled Infuse Magic. This feature allows the Artificer to implant a spell into an item for later use by anyone with an Intelligence ability score greater than 6. I'm unsure of whether the activated spell should use the Artificer's concentration or the users.

On one hand, using the artificer's concentration seems problematic. A player could unknowingly end the effects of an important spell on an ally by hijacking the artificer's concentration.

On the other hand, using the user's concentration means the artificer can have multiple helpful effects active at one time, something no other class can do. This may be the intended power level, but it could also be considered overpowered.

I know that Unearthed Arcana is playtest material and is not in a finished, polished state. This problem may be resolved in a future rework of the class.

What I'm looking for is an answer that specifies which character's concentration should be used for spellcasting from an imbued item, citing a definitive source, such as a statement by the designers, a rule I may have missed in the spellcasting rules, or something from the UA article itself.

Answer 1

It follows the rules of use magic item, so the person with the item's concentration. As the SRD (and DMG p. 141) states:

Some magic items allow the user to cast a spell from the item. ... the user of the item must concentrate if the spell requires concentration.

This follows with Mike Mearls Twitter post (while Mike isn't offical RAW, we are talking about UA material he had a hand in writing, and it does follow rules for other activated magic items):

whoever activates it must concentrate

https://twitter.com/mikemearls/status/818582158994325504?ref_src=twsrc%5Etfw

Answer 2

The rules basis is ambiguous, but developer commentary says the user concentrates

The text of the feature states (emphasis added)

Any creature holding the item thereafter can use an action to activate the spell if the creature has an Intelligence score of at least 6. The spell is cast using your spellcasting ability, targeting the creature that activates the item.

However, compare this to the Ring of Spell Storing, which is much the same idea: (DMG 192)(emphasis added)

While wearing this ring, you can cast any spell stored in it. The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as ifyou cast the spell.

The main difference here is the wording difference between "activate" and "cast". Strictly from those words, it seems that activating a spell means that it's 100% from the original caster, including the concentration; the effect of the spell is simply delayed. On the other hand, casting a spell means that the user of the item is casting the spell de novo, and thus the user must concentrate.

On the other hand, a different PC forcing the artificer to concentrate on a spell at some random time seems pretty broken, as you point out.

Mike Mearls says that the user is the one who concentrates, and that's likely the intention. I'd speculate that resolving wording issues like this is one of the goals of publishing UA as playtest material...