CyanogenMod has announced the availability of the CM11 nightly builds for the HTC One (M8). The builds will be available by way of the CyanogenMod download page and users should be looking for the "m8" designation. There will be a total of six versions available so you'll need to find your specific model number.
Details coming from the Google+ CyanogenMod page offer the following for model numbers; 0P6B10000 International, 0P6B12000 AT&T/Dev Edition, 0P6B13000 T-Mobile, 0P6B16000 Telus/Rogers, 0P6B20000 Verizon Wireless and 0P6B70000 Sprint.
If you happen to already be running a custom recovery it must report as being compatible with the following; m8, m8wl, m8wlv, m8vzw, m8whl and m8spr. Perhaps most important here -- flashing any custom ROM requires some knowledge and some patience. Simply put, make sure you know what you are doing before you begin. You will also want to make sure everything is backed up before getting started.
As far as the nightlies go -- these are just as the name would suggest, and are rolled out with recent changes. Those using a nightly build are getting the latest, but something that may also not be the greatest. You could experience some bugs or other issues. That may limit CM11 for some HTC One (M8) users for now, but rest assured in knowing more stable builds will follow.
We have yet to hear officially, but one can hope we'll see a CM11 M7 build for the HTC One (M8) available in a few weeks time. This goes back to the recent CM11 M6 release which also brought news of the two-week release cycle.
Download: CyanogenMod Download Page