CodeHS Python courses created prior to 2020 use Python 2.7 as their programming language. CodeHS Python Courses created after 2020 use Python 3 as their programming language.
Python in the Sandbox IDE
Python 3 is also supported in the CodeHs Sandbox. The CodeHS Sandbox also supports Tkinter (named Python Graphics) and Pygame. You can explore all the different types of Python programs supported by the Sandbox here.
CodeHS is working on building a future code server runner that will allow you to select what version of Python you'd like. Keep on the lookout for it in future announcements!