I did not find it in backports. The situation should be rather stable, tracking here, but I cannot find instructions for the installation in Debian. I cannot use Ubuntu's instructions like here, because they do not work.There are general installation instructions in Debian's wikipage Gnome.There are possible some complications of Gnome 3.14 in some applications (etc Matlab 2016a/b here), which is the reason, I need to test and run the newer Gnome. I do # https://wiki.debian.org/Gnome$ apt-get install aptitude tasksel$ tasksel install gnome-desktop --new-install$ gnome-session --versiongnome-session 3.14.0I contacted #debian-gnome in Irc, and they say you cannot install Gnome 3.20 in Debian 8.5 stable. You can do it however in Debian 8.5 testing.  you cannot switch back-and-forth between stable and testing Debian. It seems you have to make a new installation separately for Debian testing. PlanFixed at least when Debian 9 is released with GNOME 3.22 i.e. next year (Feb. 2017).  OS: Debian 8.5 64 bitLinux kernel: 4.6 (backports)Current Window manager: 3.14    
How to Update to Gnome 3.20 Stably in Debian 8.5?
debian;gnome
GNOME 3.20 is only available in Debian testing, so you can:update to testing (which isn't recommended as it isn't stable)install only gnome from testing (which can create new problems as gnome has many dependencies and mixing releases isn't recommended (see Debian Wiki)use a different distribution which is using a newer GNOME version.try to find out if you really need GNOME 3.20 or you can resolve your problems with 3.14wait until the current debian testing (stretch) becomes stable