What happens to breastplate Armor when it is chosen as Armorer Artificer's Arcane Armor?

Question

Ok now a breastplate is just the chest piece and maybe the shoulder guards. But as an Armorer's Arcane Armor the armor encases the user as stated by, "expands to cover your entire body". Does this change this Breastplate to a set of fullplate, and looses all Dex bonus to AC, have disadvantage to Stealth checks and now counts as Heavy Armor?

Answer 1

The only changes to the armor are those listed.

In particular:

You gain the following benefits while wearing this armor:

• If the armor normally has a Strength requirement, the arcane armor lacks this requirement for you.
• You can use the arcane armor as a spellcasting focus for your artificer spells.
• The armor attaches to you and can’t be removed against your will. It also expands to cover your entire body, although you can retract or deploy the helmet as a bonus action. The armor replaces any missing limbs, functioning identically to a limb it replaces.
• You can doff or don the armor as an action.

Further changes are detailed in the Armor Model feature. The armor retains all of its properties, and gains the additional properties stated. Since it does not state that it changes the AC or type of armor, only that certain features are gained, your breastplate is still a breastplate.