Updating Flatpak framework version

[mpanhans]

Is it possible to upgrade the flatpak platform version on elementary? And if so, how would one go about it? Or would such an upgrade ever come through the regular system updates?

When I run flatpak --version I see that I am on 1.12.7. I would like to use some applications that require features available only in 1.14.x (currently the latest branch) and 1.15.x (current the development branch).

[mpanhans]

I have answered my own question. If not added yet, first add software-properties-common, or you will get the error that add-apt-repository not found:
sudo apt-get install software-properties-common

Then add the flatpak ppa which is more up to date than the Ubuntu distro version
sudo add-apt-repository ppa:flatpak/development
sudo apt update

Then reboot. Now flatpak --version says 1.15.4. Alternatively you could add flatpak/stable, which at the time of writing would give you flatpak version 1.14.