See, this gives me pause.
Real pearls in a necklace are never all the same size. The fact that they are all completely round and all the same size (and that their color and luster are the same, and no overtones) makes me think they may be imitation.
I don't think they are akoyas. 9.5-10.0mm is the uppermost standard range for a strand of akoya pearls because the oysters are small. They would not all be the same size.
South Sea pearl necklaces are generally somewhat graduated; a difference of 1-2mm from the smallest to the largest would be a common graduation.
Freshwater pearls are also not all the same size and often not fully round, although there are bead nucleated strands-- but again, you would expect to see some size variation.
I know the clasp is gold but any clasp can be placed on any pearls (I have imitation pearls that came with an 18K gold clasp), and the way they attach to the clasp is also not something I've ever seen with real pearls.
Here is another test: the temperature test. Do you have any other pearls for comparison, whether pearls you know for sure are real--or that you know for sure are fake? Real pearls are cooler than imitation pearls that are made of glass or plastic (but so-called "shell pearls", imitations with a bead made of shell, are the same temperature as real pearls.) If the test strand and any other pearls you have are in the same room/same ambient temperature, touch them to your lips briefly. What do you feel? Then do the same with the other pearls you may have. What do you feel?