Robert A. Barr wrote:

I installed a brand new GE (Rheem) electric water heater about 4 months
ago. Recently I've noticed a slight (but strengthening) smell of sulfur
when I run hot water anywhere in the house.

Years ago, I had a problem with a really strong sulfur smell from the
hot water, and it turned out to be the sacrificial anode. Could that be
the problem already?

The anode may encourage the odor formation but the underlying cause
is far more complicated.
Go he
http://www.ho****er.com/techhome.htm

Click on the FAQ.

Substituting an aluminum anode may help, but I don't know
if that will affect the warranty.

As Gary Slusser will tell you, the real fix is to treat the
water beforehand so that the conditions for odor generation
don't exist.

Jim