The copy is created in and cast from exile. You cast the copy during the resolution of Arcane Savant's last ability. You ignore any timing restrictions based on the card type of the card you copied. However, you must still follow any other timing restrictions, such as "Cast [this spell] only during combat."

If the copied card has {X} in its mana cost, you must choose 0 as its value when casting the copy.

You can't pay any alternative costs the card has. You can pay additional costs, and if the spell has any mandatory additional costs, you must pay those.

As Arcane Savant's last ability resolves, if there are multiple cards you exiled with cards named Arcane Savant, you choose one of them to copy.

If you have more than one Arcane Savant in your deck, you may reveal any number of them and exile that many instant or sorcery cards you drafted that aren't in your deck.