OK, so the calendar I checked from Wizards only listed Underdark, but apparently there’s a second book out this month: Player’s Handbook Races: Dragonborn
New options and character hooks for dragonborn characters.
If you want to play the ultimate dragonborn hero, this book is for you!
This expansion of the Player’s Handbook® core rulebook explores the mysteries of the dragonborn. It presents D&D® players with exciting new options for their dragonborn characters, including unique racial feats, powers, paragon paths, and epic destinies. This book also includes ways to flesh out your dragonborn character’s background and personality.