A GWAC is an IDIQ built specifically for information technology, awarded by one agency but usable by any federal buyer. SEWP, CIO-SP, and Alliant are the names you will hear most. Getting a seat is competed like any other IDIQ; after that, the work arrives the same way it does on any multiple-award vehicle, as task orders you compete for against the other seat holders.

In a sentence

"This requirement will be competed among SEWP V contract holders." Only businesses that already hold a seat on that specific GWAC are eligible to respond, so the competition that mattered most already happened when the vehicle itself was awarded.