Nightly builds for CyanogenMod 10.1 are now available for the HTC One, at least for GSM and Sprint versions of the phone.
The builds aren't quite stable yet, so people looking to flash and forget should hold off for a while. Audio on outgoing calls is iffy for now, but incoming calls seem to be working fine.
"The HTC One repo's have been opened on our Github organization and are now available for syncing. The repos support the GSM (m7) and the Sprint (m7wls) variants of the HTC One," says the CyanogenMod Google+ page.
CyanogenMod 10.1 is based on Android 4.2.2, a build slightly more recent than the stock Android 4.1.2 that comes with the HTC One. It also lets users get rid of BlinkFeed, a new feature on Sense 5.0 that has received mixed reviews. However, mods are made at your own risk, and it does void the warranty, so root with caution, and only if you know what you're doing.
Unfortunately, AT&T users may not be able to use any custom ROMs in the future. AT&T has already announced that it will not unlock the bootloader on HTC One devices it sells, a prerequisite for rooting the phone. The only other option for AT&T customers is to pick up an unlocked 32GB One directly from HTC. There's also a 64GB unlocked developer's version, though supplies are limited, so you'll be lucky if you can get your hands on it.
The HTC One features a 1.7GHz quad-core Qualcomm Snapdragon 600 processor, 2GB of RAM, a 4.7-inch 1920x1080 pixel widescreen Super LCD 3 display, a 2300 mAh Li-Po battery, a 4-megapixel "Ultrapixel" camera with enhanced low-light sensitivity with 1080p HD video, up to 64GB of internal storage and runs Android 4.1.2.
Check back for the latest updates on the HTC One as they become available.