The Library at Hellebore by Cassandra Khaw

The Hellebore Technical Institute for the Gifted is the premier academy for the dangerously powerful: the Anti-Christs and Ragnaroks, the world-eaters and apocalypse-makers.

Hellebore promises redemption, acceptance, and a normal life after graduation. At least, that’s what Alessa Li is told after she’s kidnapped and forcibly enrolled.
But the Institute is more than just a haven for monsters. On graduation day, the faculty embark on a ravenous rampage, feasting on their students. Trapped in the school’s cavernous library, Alessa and her surviving classmates must do something they were never taught: work together.

If they don’t, this school will eat them alive…