It's the same HTC One you know and love, with a healthy dose of unlocked
Fancy getting yourself a developer edition HTC One? The official word from HTC is that they will be available for preorder starting at 10 am Eastern time today (April 5). The phone will have identical hardware to it's carrier-provided brethren, but have the SIM card and bootloader unlocked out of the box. The price is set at $649 for the 64GB version. You'll find more information when it goes live at HTC.
On the radio side, the developer model will support AT&T HSPA+, T-Mobile HSPA+ in the 1900 MHz band, and LTE on 700/850/AWS/1900 Mhz. Users on T-Mobile in areas where 1900 MHz hasn't been repurposed (read: most everywhere) will only be able to get EDGE or LTE (if available).
It's important to note that we don't know if the carrier version in the US will be supported on the HTC developer unlock site, so this may be the answer you're looking for. Also we don't yet know when these will ship, but the unofficial word is April 19.
Source: +HTC Dev