https://getfedora.org/static/images/workstation/workstation-...
https://getfedora.org/static/images/workstation/workstation-...
You can tell from some hints of red highlight on the trackpad where the buttons on the old X1 are.
Other indicators are the keycaps, webcam position, and screen rim being identical to the X1.
There's also the oddly clipped fingerprint reader off on the right side, and the fact that the X1 has a somewhat unique profile. Here's a comparison picture of one not shooped up: https://blog.hboeck.de/uploads/x1carbon.jpg
2nd gen has the 'Fn' key but still has the fingerprint reader on the right margin like the 1st gen. 2nd gen is also distinguished by having the split middle button on the trackpad.
3rd gen (the current one?) moves the fingerprint reader below instead of to the right from the keyboard.