2010 Giant Anthem X2 stem

[shortleg]

Hi all. I just want to know what diameter is the stem fitted in to the bike. I'm thinking if changing the stem from 100mm to something shorter 60mm to 70mm. I do mainly XC riding and maybe some DH with no more than half meter jump. I just want to have a little bit more responsive around tight bends

[Duck!]

1 1/8" at the steerer & 31.8mm at the bar.

With its 71 degree head angle - considered exceptionally steep by modern MTB geometry standards - the Anthem is already a very responsive bike. Making it any twitchier is going to make it even harder to ride than it already is on technical descents.