I had the same question, and I wanted to order one to have it ready to go for launch day. Please read below for Mophies response:
Thank you for contacting mophie.
We're excitedly awaiting the arrival of the iPhone 5S, and we'll release compatibility information once it is available. The best way to keep up to date on new products and product compatibility is to join our newsletter at mophie.com/newsletter.
mophie loves you
Thank you,
Tara Brooks
mophie Customer Service
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I guess ill just have to wait and see.