Robe of the Archmagi
Wondrous item, legendary, requires attunement by a sorcerer, warlock, or wizard · 2014 rules, SRD 5.1
No armor: AC 15 + Dex mod; advantage on saves vs spells and magical effects; spell save DC and spell attack bonus +2.
Also in the 2024 rules (SRD 5.2).