Do the 2019 UA Artificer's Alchemical Homunculus and Iron Defender companion creatures get death saving throws?

Question

In the May 2019 Unearthed Arcana update, two of the four Artificer specialist options can summon constructs as companions: the Alchemist summons an "alchemical homunculus", and the Battle Smith summons an "iron defender".

Unlike the Artillerist's turret, which is a magical object, these companions are considered creatures, and there is no text that says specifically what happens when they are reduced to zero hit points. If they die, reviving them requires expending a spell slot, so, I want to know how easy it is for them to get killed in battle.

When one of these constructs is reduced to zero hit points, does it die immediately, or does it start rolling death saving throws like a player character would?

Answer 1

Rules as written, the DM decides

Monsters and Death:

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

However, there is unofficial clarification from Mike Mearls on twitter (Sage Advice, Twitter) for the Revised Rangers companion, where he says they do get saving throws:

@tobyfernando Does the new BM Ranger companion get death saving throws upon reaching 0 hp?

@mikemearls yes

See also this similar question relating to the Revised Rangers companion

Answer 2

The default is that only PCs get death saving throws

NPCs are dead at 0hp unless the DM decides they aren’t.