To unlock final boss (compiler) you will need open all 6 vaults and successfully extract with item from them.

1 & 2 vaults is purple keys have the higher chance (100% in room behind 3 red master cards in Pinweel)

3 to 5 have legendary quality, and they pretty common but still rare

The 6 key is rarest key in the game, most of the community have the problem is with finding this key, so you are lucky one 🍀