Yes, I think it is the first stabilized MF optic. That should be a nice boost for anyone who uses this lens, on top of a reasonably fast aperture. I'm interested to see it get into the market and see how it performs, since I hand-hold my 645D all the time and miss the stabilization. I'll probably keep my 645 A 120mm f/4, 67 90mm f/2.8 and 67 105mm f/2.4, because I really like all of them. But this new entry piques my interest.
The downside, of course, is that it implies we're not going to see in-body stabilization in a future 645D sequel, at least not any time soon. If we were, I can't see Pentax designing in-lens stabilization for this one... what, just to please existing 645D or older 645 film shooters? Don't think so -- it signals a strategy to keep stabilization in the lens. At the kind of prices we're seeing for the new 645 lens designs, it's going to put a further dent in the affordability and/or utility of the system for anyone more budget-minded. I say that as somebody who has sprung for a pair of 645D bodies so far, a DA 25mm, a "new old stock" FA* 300mm and some other bits & bobs to go with all my bargains from eBay and KEH. I don't question the Pentax's value in the MF context. But I was really hoping for in-body stabilization (among other hopes for a 645D II) because I'd like the edge in low light situations in several useful focal lengths, without having to extend my eventual retirement by another 20 years.
Oh well... it's only money.