The HTC One M8 from 2014 will get Android 5.1 Lollipop and Sense 7 in August. This info is according to the official HTC Twitter fpr the United Kingdom.
@squishybytes Android 5.1 and Sense 7 will be released on the HTC One M8 in August 2015. Nothing has been confirmed with the HTC One M7
— HTC UK (@HTC_UK) 29 abril 2015
While there’s no firm date for the 5.1/Sense 7 update on the HTC One M7 from 2013, at least they mentioned it. The M7 will be more than two years old at that point, which is when most manufacturers tend to drop off software support.