HTC takes the Developer Edition HTC One pretty seriously. The company has been good about pushing updates to the device, and now the full Android 4.3 ROM can be downloaded as a ZIP from the HTC Dev website. That's more service than even the Google Play Edition HTC One is getting.
Update: The Android 4.3 RUU has now been posted as well.
This isn't just the kernel source, which is what OEMs have to post when they release a new build of Android. HTC has chosen to include everything you need to flash the phone – the entire factory system image. Of course, it'll take a little knowhow to get that done. If you want to tinker around, the download is 1.1GB, and there is also a build of Android 4.1.2 if you like it old school.