De acordo com Jeremy Crawford :
I'd allow a pearl of power to take an expended spell slot of 4th level or higher and turn it into a 3rd-level slot.
Parece um compromisso razoável recuperar os slots de nível inferior antes do próximo descanso breve.
A partir do primeiro conjunto de erratas para o DMG , esta é agora a resposta oficial também.
Pearl of Power (p. 184). The first sentence is now two sentences: “While this pearl is on your person, you can use an action to speak its command word and regain one expended spell slot. If the expended slot was of 4th level or higher, the new slot is 3rd level.”