Yes, iPhone 6s Apple-branded cases will work with the iPhone 6

[iMore.com]

Apple has already begun updating their Apple Store displays in preparation for this Friday's iPhone 6s and 6s Plus launch, and one casualty: A surprising lack of "iPhone 6"-branded cases. The good news: Those 6s and 6s Plus cases work fine with the 6 and 6 Plus.

Full story from the iMore Blog...