Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter: Hands-On [PICS]
Here's a quick look at Apple's Thunderbolt 3 to Thunderbolt 2 adapter.
Adapter
Apple Support Page Outlines Thunderbolt 3 Adapters for 2016 MacBook Pro
Apple has released a support page that outlines different adapters users can purchase to connect with Thunderbolt 3.
Apple’s Solution for Removing the 3.5mm Headphone Jack is Another Adapter
Daring Fireball's John Gruber hopes that Apple does not decide to go with an adapter.