From the Publisher's blurb:
Flux elementals, lightning drakes, scornful undead, and diabolical burnination!
In Sorcerer Summoning, Rob Heinsoo introduces all-new spells that connect with the sorcerer’s heritage talents. Summon powerful elementals, or an undead courtier of the Lich King who unleashes both damage and withering snobbery on your enemies.
Wield the sorcerous heritage of the Three to call forth an electric stream of lightning drakes!
Summon the Diabolist’s burnout elemental, and learn the true power of spell frenzy!
Tap the arcane magic of the Archmage and unleash bizarre flux elementals to demolish your foes!
Call up the Lich King’s undead toadies, who will demonstrate in word and deed why their master is the true ruler of the Dragon Empire!
All this, plus a detailed update of the overall summoning mechanics in 13th Age.