The last Black Series Prototype Boba Fett was in 2014, stood 6" tall, and was a Walgreens exclusive.
According to Yakface, this line is actually re-packs of previous 3.75" figures, which include already an older Prototype Boba Fett from 2011, which is already a re-paint of their 2004 Boba Fett (VOTC) with a belt/holster piece from a 2007 Fett.
Helmet nod to jeradchil on Twitter for the heads up and Kelton Slaton on Facebook for the re-pack points.
An official press photo has been released:
It's due to be released this Spring.