I know you said latest, but which latest? The 12 speed Di2 or the 11 speed Di2?
Just like anything else, you have to know what model and version of Di2 you are talking about. For the last few versions of 11 speed Di2, it can be fully contained inside the frame and bars of the bike. If you didn't see the LED's and button neatly slid into the end of my right handle bar end, then you would only know it's Di2 from looking at the DR's. All 11 speed Di2 requires an optional component to be purchased to have wireless functionality with other things such as your Garmin or other device.
I bought a
EW-WU111 to use with the Di2 on my Tarmac. I connected it as the first connection inline to my battery which is inside my seat tube. Being a carbon bike, I haven't had any issues with it being seen by my Garmin on the handlebars. Haven't heard if others with aluminum or other materials for their frame have issues doing such.
12 speed Di2 has the wireless included since it doesn't connect everything with wires.