CyanogenMod 10.1 nightly builds of stock Android 4.2 now available for the HTC One
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Dubbed M7, after the codename of the device in the development phase, they are as usual the case with early builds not entirely stable, but good enough to play around with if you know what you are doing. Outgoing audio is the big issue at times, but also the Wi-Fi calling on T-Mobile, and the IR blaster.
Still, if you want to see how your HTC One looks like debloated from Sense 5.0 and BlinkFeed, with close to stock Android 4.2 experience, head over to the source link after you've unlocked the bootloader, rooted and installed CWM recovery with this simple tool.
Things that are NOT allowed: