Not released, but speculation. An origin character is a spawn whose master is a vampire. Vampires are listed as a CR 13 enemy in 5E, thus I would assume that this origin character's master is within such a range.
Well even if that is the case, it could be an optional boss fight. A party with strong lvl 10 characters can take on a CR 13 enemy. On my tabletop game my lvl 6 party killed a Death Knight (CR 17).
