According to @HTC_UK Twitter account Android 5.1 with Sense 7 update for HTC One M8 will be available in August 2015.
Given HTC’s history it will probably be last week from August so we still have about 4 months to wait. Hopefully some leaks will pop up earlier and until then at least we have HTC One M9’s Sense 7 running flawlessly on HTC One M8
https://insertcoin-roms.org/wp-content/uploads/site2-1-300x84.png00baadnewzhttps://insertcoin-roms.org/wp-content/uploads/site2-1-300x84.pngbaadnewz2015-04-29 14:00:412015-04-29 14:48:46HTC One M8 Android 5.1 and Sense 7 Update Date
Here are some interesting links for you! Enjoy your stay :)