The stem is 145g, so a little weight might be able to be saved there, but Giant uses a 1 1/4 steerer tube, so that really narrows your choices.
The handlebars are definitely heavy. The New Ultimate EVO bars would save you around 110g.
Wheelset isn't exactly light, but not a complete boat anchor either. Crests laced up to American Classic hubs would save you around 220g.
Formula R1's can be had for pretty cheap on Ebay and would save quite a bit of weight.
The Giant Anthem Advanced 0 comes in at 22lbs and pretty much every component is lighter, so expect to spend quite a bit of money if you're wanting to drop significant weight.
I weighed the new handlebars I got (Giant Contact SLR Riser) at 175g. I know I could go lighter with a flat bar, but comfort is key to me.
I do not know if Giant offers their carbon-rim 27.5 wheelset seperately yet...I'm afraid to ask how much.
I will look into the Formula R1s...I'll have to get some sort of mounting clamp for the XT shifters since they're integrated into the brake levers.
I didn't want to spend the extra $3000 for the Anthem Advanced 0 27.5 since it wasn't Shimano (it's 1x11). I may be stuck with a 23.5-24 lbs. bike with changes in wheels and brakes.