HTC One (M8) on AT&T to begin receiving Android Lollipop update tomorrow
Often, AT&T only allows update queries to be made once every 24 hours so instead of hammering your "system update" button, wait until tomorrow. According to HTC's Mo Versi, specifically after 10:00am Pacific on Tuesday, as that is when M8 users can expect to start seeing update notifications.
It is always good when a plan comes together, and HTC has put forth a good effort to update its devices in a timely manner following major releases from Google. The HTC One (M7) on AT&T was released a week ago, and Tuesday’s update for the M8 follows in-kind.
source: Mo Versi (Twitter)