@rogzilla71 @jmjm @phooky It was an 8086 (or 8086 clone), just running at a higher clock speed (internet claims ~7MHz, I remember 10MHz for some reason). Apparently AT&T had very little to do with it other than the sales channel; it was a rebadged Olivetti M24.

They're on ebay, but even at $50 not really worth it:
https://www.ebay.com/itm/Vintage-AT-T-Personal-Computer-6300-Olivetti-M24-PC1050-Motherboard-8086-CPU/312171727796?hash=item48aee28bb4:g:9ooAAOSwPI1axrrP