Hi Michel,
Yes, you are right. Segment will be automatically installed with an upgrade to 4.7.7. However, it's already available for 4.5.x - 4.7.6.x versions. Here you can find the installation packages for X-Cart 4:
https://secure.x-cart.com/?&area=filearea&target=files_explorer&folder_id=24 5419 So there're two options for you - wait for the upgrade, or install the addon now on your existing X-Cart version.
Have a nice day!