I decompiled the clock SWF on ATI's home page(sad i know)anyway it says"Radeon X1K Enter a World of Visual Velocity"
I've posed a screenshot at the bottom of page.
Following ATI´s previous naming/numbering scheme,i believe the X1 to be read as eleven,the k as thousand.
Example:
Radeon series: 7000,8000,9x00,X8 (X=10 in the latin alphabet ie X800=10800) and now X1=11 in the latin alphabet ie X1800=11800.
Seems a natural progression,yes?
Decompiled clock SWF/ATI's home page
Now all i have to do is wait for 5th october......to realise the 7800gtx pwns ATI's offering!

only jk'ing,i know where my £'s going regardless of benchmarks/overdue forceware 80's.