Not sure when this came out, I believe late 2015 but the earliest I can find anything about it is early 2016. It was included in a collector's edition. The inside of the Mini SteelBook has slots for holding multiple Vita games as well as a few microSD cards. This may be the first commercially available Mini SteelBook.
Pics are courtesy of jahonius88 on PSNation.com
Pics are courtesy of jahonius88 on PSNation.com