For the Pi-top version 2.
If you use the new Pi 3 model B+, processor is a little bit higher, you need to change the conductive cooling tape thickness, then it will fit.
Pi-top OS is not working although updated via update, upgrade, dist-upgrade, does anybody have an advice?
So at the moment I use standard Raspbian, then it works perfect.
The new Pi 3 model B+ also works fine on my pi-top using the latest Raspbian Stretch and the pi-top device management software (see github.com/rricharz/pi-top-setup for installation instructions). The reason why pi-topOS currently does not work is that the current version of pi-topOS is still using Raspbian Jessie. Just be patient until pi-top has moved their OS to Stretch. They are advertising and selling now the model B+ and therefore a new OS version can be expected rather soon.
I also found that the stock thermal pad was a bit too thick with the Pi 3 B+.
I removed the original pad and replaced it with a thin one I had. I would think a small dab
(very small) of thermal compound would work just as well if you dont have a thin thermal pad.
I also found that Polaris does not run but Raspbian stretch does.
Note: an updated Raspbian stretch was released on March 13 that added support for the Pi 3 B+
2018-03-13: * Raspberry Pi 3 B+ support * WiFi is disabled until wireless regulatory domain is set (Pi 3 B+ only) - The domain can be done through 'Raspberry Pi Configuration' (rc_gui), 'raspi-config' or by setting 'country=' to an appropriate ISO 3166 alpha2 country code in /etc/wpa_supplicant/wpa_supplicant.conf.