According to Shimano its the 10-51 that is 470g:
To Build Closer Relationships between People, Nature, and Bicycles. We believe in the power of cycling to create a better world as we move forward. We inspire all people to enjoy our products in their everyday lives and where they take them.
bike.shimano.com
Either way, i have been able to cancel the XT cassette as part of my order, and will get an NX cassette for now. Probably go to the XT eventually, but for now getting the bike built is preferred.