If you’re looking for a workaround to the SSH host key validation issue in Xcode on macOS 26.3, we’re seeing evidence that this works

What appears to have fixed it for me was copying the relevant lines from ~/.ssh/known_hosts into /etc/ssh/ssh_known_hosts

Update: verified that this fixed it for some colleagues as well. Ensure that the file has ownership root:wheel and permissions 644, and pay attention to the file name (ssh_known_hosts, not known_hosts).