Since Windows 10 1803, a built-in/optional OpenSSH implementation is included with Windows, including a SSH agent service. I've configured git to use this OpenSSH by adding this to my .gitconfig:
[core]
sshCommand = "C:/Windows/System32/OpenSSH/ssh.exe"
Sourcetree however, seems to only want to use either Pageant or the OpenSSH agent bundled with Git. Anyone know of a workaround, or do we just have to wait for Sourcetree to support the built-in OpenSSH implementation?