Just a couple weeks ago, HTC sent the Sense 6 Lollipop update to owners of the unlocked and developer editions of the One M8. Now, the kernel source for those devices has been posted to the HTCDev website. Remember, this is not the same as the Lollipop kernel source published well over a month ago for Google Play Edition devices; this is for phones running Sense.
For most users, there's nothing to see here. Don't rush off to download because there's nothing of direct use to you. However, custom ROM development relies on resources like this so you may benefit indirectly if you like to flash third-party software on your M8.
While the carrier is listed as "Brightstar US," there is no such carrier. Brightstar is a hardware distributor and we have come to realize that this is just HTC's way of saying it is for GSM unlocked phones. AT&T and T-Mobile sources will be posted when that software is finished, but this kernel will be used in development of ROMs that will run perfectly fine on GSM carrier phones.