Carriers often get agreements with smartphone makers so that they can have certain models exclusive for themselves or get different kind of versions of the phone by modifying certain aspects of it, from the placement of the logo to changing some of its specs. Sony doesn't have the best reputation among carriers in the US, as the company has opted to sell their devices unlocked in their own site, which probably has affected their sales. Since Sony has made clear that they won't quit the mobile business, they probably would want to make some changes in their sales strategy to reach as many users as they can.
Verizon has been having some exclusive models from Sony in their portfolio and last year, about a month after the company unveiled the Xperia Z3, the carrier announced that they would get a device called Xperia Z3v. Its design had a stronger resemblance with the one sported by the Xperia Z2 (although it was larger, thicker and heavier), but its internals were more like the ones of the Xperia Z3. Recently, a similar strategy was used as the Xperia Z4v was announced as a variant of their most recent flagship for this carrier, only this time, the difference is more significant because it is the first smartphone of the company to include a QHD display and at 5.2 inches, it turns out to a density of 565 ppi. The design also had more changes as the top bezel was reduced making it a little shorter but still it is heavier and thicker than the Xperia Z3+ (aka Xperia Z4).
Today it was reported that the Xperia Z4v would be available on August 13 as suggested by an official looking microsite, but now it is reported that the public relations agency in charge of Sony's mobile division in North America has mentioned that the information from that microsite is not accurate and that no official information has been given regarding the launch date of that smartphone, so they couldn't give an estimate as to when to expect the availability of the handset. When it was announced the Xperia Z4v was said to launch during the summer, so it could be a little sooner or all the way up to September.