A developer article on IBM's website was noted to have a reference to a yet-unreleased processor referred to as the PowerPC 970GX.
"The only processors currently supporting AltiVec are the G4 and G5. The G4 (including model numbers 7400 and 7410) and G4+ (7450 and 7455) processors are made by Motorola. (There are more models than just the ones listed here, but these are the most widely discussed.) The G5 chips include the IBM 970, 970FX, and 970GX; these are essentially POWER4 cores with an AltiVec unit bolted on."
The reference has since been removed from IBM's site. Information on the 970GX was first leaked back in November 2004. It was described with a larger L2 cache, 3GHz speeds, and an expected ship date in early 2005.
Update: The page linked above has been modified with the following editor's note:
"Our apologies!
The original version of this article contained an erroneous reference to a "970GX." We apologize for any confusion this may have caused.
--Editors