Dave Zatz had a nice find over at the FCC today, uncovering what looks to be possibly a third generation Nest learning thermostat.
The device looks like it will have 5 GHz Wi-Fi, which is interesting in and of itself. Adding 5 GHz could signal they have intentions do something interesting with Wi-Fi operating in this higher band, but the more likely answer in my opinion is they're simply using the latest Wi-Fi chipsets using 802.11ac, the latest Wi-Fi spec which operates exclusively in the 5 GHz band. Of course, all Wi-Fi chipsets nowadays are backwards compatible with the older specifications, so this Nest will most certainly work in the 2.4 GHz band over 802.11n or 802.11g.
Dave also points out the numbering convention indicates this device definitely looks to be a Thermostat, which as this device is called the ZQAT30, while the second gen Nest thermostat was the ZQAT20.
Another potentially interesting question about this new product are whether it will use Brillo/Weave technology. While Nest is operating out of the new Alphabet parent company and the effort around Brillo and OnHub are driven out of Google, it's clear there is some level of cross-fertilization of technology. Illustration number one of this cooperation is the fact the OnHub includes a Thread radio (Thread's origins are out of Nest).
Brillo/Weave are software-centric upgrades, so it would be hard to tell from FCC docs whether the new Nest thermostat is build around Brillo, but my guess would be that this device does indeed use Google's new Android IoT stack. One reason I think this is a possibility is the company delayed shipping a new thermostat at their July presser, while they did ship new a new Protect and a Nest Cam.
Hopefully we'll know more soon!