Debian Stretch OK - where is Python3?

It seems after installing the latest December image and updating via SSH (on a headless RPi3), only Python2.7 exists on the system.

I expected after the Stretch update it would be Python3.5 or both. Should it be present or should I install it manually?

I thought it was installed by default:

osmc@yeti:~$ python3
Python 3.5.3 (default, Jan 19 2017, 14:11:04) 
[GCC 6.3.0 20170118] on linux
Type "help", "copyright", "credits" or "license" for more information.

If it isn’t:

osmc@yeti:~$ sudo apt install python3

I know how to install it but I expected it to be part of Stretch. On a clean system it says

osmc@RaspberryPi:~$ python3                             
-bash: python3: command not found

Ok, I guess it isn’t installed by default. I checked another one of my systems and it isn’t installed. I must have added it sometime in the past to the system I checked on.