Archwizard's Spellcraft

You command the most potent arcane magic and can cast a spell of truly incredible power. You gain a single 10th-rank spell slot and can prepare a spell in that slot using wizard spellcasting. Unlike with other spell slots, you can't use 10th-rank slots with abilities that give you more spell slots or that let you cast spells without expending spell slots. You don't gain more 10th-rank spells as you level up, but you can take the Archwizard's Might feat to gain a second slot.