Nice, thanks. I knew there was a patch, didn’t know it was on shipping on standard distros
In my memory, the patch was not in upstream and even more far away from distro packages at the time tmux came alive.
I also went with tmux for vertical split (left-right panes)
screen is gpl, tmux isn't
As an end-user though, it doesn't usually matter.
As an end-user, what software you choose to use is a form of advocacy for that software and its license. So it does matter, but you can choose to not care.
Note for others: tmux is under the ISC license, a permissive non-copyleft opensource license.