Vaultborn Tyrant token has a CMC.
*** BUG REPORT ***
"Vaultborn Tyrant" - The triggered ability after killing it is NOT creating a token with a 0 CMC of the creature. It is returning the creature to play as if Cloudshift or Momentary Blink. The graphic on the screen is a "token" but the underlying properties are not. I should not take damage when killing the token with "Feed the Swarm".
ATTACHED Screenshot - My opponent cast Vaultborn Tyrant and passes turn. I have 13 life and 2 copies of Feed the Swarm in hand. I cast 1st copy on the cast copy of Vaultborn Tyrant and take 7 damage leaving me 6 as a life total. I cast the second copy on the token, take 7 damage and lose the game at a -1 life total.
This can be reproduced and there is an additional complaint on the same issue if one searches this forum.

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Rezzahan#77802 commented
"*** 706.2: When copying an object, the copy acquires all copiable values of the original object's characteristics.
Thus, a "token" has no mana cost, but a "token copy" will have the associated mana cost (and all other copiable values) of the original object it is a copy of. If the original object was a "token" the cost is 0 (zero), but as in the case of Vaultborn Tyrant's death ability, it is a copy of a permanent spell and will have a CMC of 7."
A small correction is nessessry here:
If the original object was a token with a mana cost, the new token copy will also have that mana cost. -
smurfus#81009 commented
@ Rezzahan#77802 -
"Nothing about tokens or in the rules make tokens unable to have a mana cost. "
This is what caused me to go look things up and your statement is not exactly correct, but mostly, sort of... I now know the difference and can add the context for any future reader of this. Maybe it will help someone learn what I just did.
*** 110.5b: A token doesn't have any characteristics not defined by the spell or ability that created it.
This means all spells or abilities that use the action "create a token", the token created does not have a mana cost unless the spell creating it stipulates it to be something other than 0 (zero). ...however... (this is the part where I learned something from all of this)
"On the contrary, mana cost is a copiable value. So any token that's a copy of something with a mana cost, will have that same mana cost."
*** 706.2: When copying an object, the copy acquires all copiable values of the original object's characteristics.
Thus, a "token" has no mana cost, but a "token copy" will have the associated mana cost (and all other copiable values) of the original object it is a copy of. If the original object was a "token" the cost is 0 (zero), but as in the case of Vaultborn Tyrant's death ability, it is a copy of a permanent spell and will have a CMC of 7.
PS - I could have done this to begin with, you forced me to get unlazy about it.
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Rezzahan#77802 commented
Nothing about tokens or in the rules make tokens unable to have a mana cost. On the contrary, mana cost is a copiable value. So any token that's a copy of something with a mana cost, will have that same mana cost.