From Cordcutters.com, quoting a Roku message to developers:
OS 7.5 begins shipping to consumer Roku devices tomorrow, and will continue rolling out in phases over the next six weeks. We’ve just updated most devices registered in the Roku Beta Developer Program to OS 7.5.0 Version #4092, which is the version being shipped to consumers tomorrow.
Roku Express, Premiere, and Ultra devices are the only exception to this build number. These beta devices are currently running OS 7.5.1 Version #4022. Note that these will be the last consumer Roku devices to update to 7.5 and firmware for these products is still in beta development. Thank you for your contributions in refining this latest Roku firmware update!
Interesting that the Roku new devices (Ultra, Premiere and Express) will be the last to see the new OS. One would have thought they would be one of the first.Roku OS 7.5 Nov 1 2016
I am not sure why that is, but I would assume it might have to do with compatibility across devices. I have a Roku 3 and I guess that the new devices have certain requirements (Features) that the R3, like I have and other previous devices doesn't have which is why the newer boxes are probably being held off as far as getting new firmware. As for me, I have thought of upgrading to the ultra at some point as I am looking to add another box to my home so others can use it, but I'm not sure what the differences are, if any compared to my R3. I have a discontinued RLT model that was my first Roku box that hasn't been in use since I upgraded to the R3 in 2014, but I don't want to move that into another room because one of the reasons I upgraded was I heard the LT was being discontinued and thus would probably not get updated firmware/software. The R3 has been extremely reliable for me and I was hoping that it would be at least 3-5 yrs, before I upgraded, but such is the trend of ever evolving technology I guess. I'm not planning on adding an Ultra to my list of devices before year's end, but it is something that I am thinking about with the idea that the R3 may become discontinued at some point as my LT was.