If you've got an HTC One M8 on Sprint, be on the lookout this morning for a system update. Sprint's rolling out software version 1.54.651.8. And while the changelog is for whatever reason vague — stability and call performance improvements, is all it says — you'll also see you now have the Extreme Power Saving mode.

This is an update we knew was coming, of course, as HTC previously told us it was waiting on U.S. carriers to approve the update that has already pushed out to non-U.S. versions of the M8.

Extreme power saving mode

Extreme Power Saving Mode is more of an emergency battery mode. It locks out most of the "smart" functionality of the phone, leaving you with a new home screen and access to only the phone dialer, and HTC's email, text messaging, calculator and calendar apps. No notifications. Not push anything. HTC says this mode can eke out some 15 hours of use on just 5 percent battery.

Look for the other U.S. carriers to push out this update in due time.

Source: Sprint; More: HTC One M8 forums Update image via @GoodByeBluMndy