Is my Apple Watch Series 4 cellular?

Series 4 was available as a GPS model, and GPS and cellular model.

As correctly mentioned above, cellular Watch models can be differentiated from non-cellular models by a red cap, or red ring, or orange ring, located on the digital crown (knob) of the particular model Watch.

Identify your Apple Watch - Apple Support

No. For reference, cellular models will always have a ring or cap on the digital crown.

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