The PS4 slim units that have been leaked into the wild for reasons that remain unknown are of the 500 GB variety, sporting product code CUH-2016A. According to Twitter user shortman82, who purchased one of the consoles, that's not the only available model.

The console manual, in fact, reveals a CUH-2016B console with a 1 terabuyte hard disk drive built in (it's worth keeping in mind that the "16" is simply the region identifier, and in this indicates a console sold in the UK).

Incidentally, shortman82 also mentioned that he did not find any reference to 4K resolution anywhere in the console's operating system or box, probably indicating that the console will still have a maximum output resolution at 1080p.