Carrier-rated against the engagement.
The contractor is the named insured on the policy — for WC, GL/PL, Media/Cyber, or whatever mix the engagement requires. WC and the liability lines are rated by state × class code × engagement value; Media and Cyber are flat per-day rates for the coverage window. Many platforms remit premium on the contractor's behalf as part of the engagement, but the structural responsibility (and the named insured) stays with the contractor.