The T-Mobile variant of the HTC One hasn't gotten an update since May, but the one rolling out now is not the fabled Android 4.2.2 out on the international version. No, this is still 4.1.2.
T-Mobile lists the following changes in 1.27.531.11:
- Software stability
- LTE and reception
- Processor enhancements
The update is 247MB, whereas the last one was 18MB. It's possible HTC made some other tweaks not listed in the changelog. Those camera and capacitive button fixes could be rolled in, for example. Although, that update was listed as a 1.29.X build on the other variants. Whatever is in there, 50% battery power is required to do the update, and rooted devices need not apply.
1.27.531.11 is starting to roll out now, and will be complete by August 9th. A manual update on HTC's site will reportedly be available, but it doesn't appear to be live yet.