One of the most interesting components of SRAM's incredibly light XX groupset was the cassette, which employed a unique one-piece construction approach borrowed from SRAM's Red road group. Now this X-Dome technology will be available in 9-speed guise.
Seven of the the cogs are CNC-machined together out of a single block of billet steel on the XG999 cassette. Weight claimed for this 11-32 cassette is just 175g.
Don't expect it to be cheap however, with a price of $300 (UK price TBC).