They’re often closely related to Zeiss still-lens designs, but cine lenses are not just identical photo lenses in a different shell.

From the community answers, the main differences are:

• cine lenses are optimized to reduce focus breathing
• they often use more iris blades for a rounder aperture and smoother bokeh
• they add cinema-oriented mechanical features like long focus throw, calibrated scales, manual iris control, and more robust housings
• coatings/internal light-control details may differ

So the glass and overall optical character can be similar, but the cine versions are typically tweaked for motion work rather than stills. In practice, the biggest differences are usually in focus behavior, iris design, and mechanics, not a completely unrelated optical formula.