"One more thing,

Skynet was concerned that the T-1000/T-X models had the capability of becoming self-aware. Making too many of these things raised the odds of this happening. Of all the Terminators Skynet was churning out, these prototype models were a threat not only to John and Sarah Connor, but Skynet as well. They were given the ability to make judgments, were creative, and had the desire and need to "live".

Supposedly a T1000000 protects Skynet's core. Here is an image http://terminator.wikia.com/wiki/Image:T-1000000.png

The T1000000 only mission is to protect Skynet. It is a Terminator in only that sense.

The T1000000 appears in "T2 3-D: Battle Across Time", a James Cameron creation for Universal Studios in Orlando, FL, Hollywood, and Japan.

Since JC created T23DBAT, the T1000000 could be considered canon.
"

"True for the T-1000, but not nessesarily so for the T-X. The T-X had a CPU, putting in more in line obedience-wise with the earlier '900 and '800s. Plus, there is nothing to indicate it was a prototype."