shared a link to a portfolio of Valve's former 3d artist Derek Jenson. In it you can find few video demonstrations of different models and their animations, including some unused ones. For example there's an old and previously unseen model of ground turret, hands animation that differs from the one in the final game, and old Combine gates model and some other ones.
You can see his portfolio following this link
from our Discord server
has done a remake of the ground turret model shown in this video. You can download the source files of his remake model following this link