HTC One series got Android 4.4 (KitKat) update with Sense 5.5 earlier this year. The HTC One, its dual SIM variant and the HTC One Max got the Sense 6 update few weeks back. Recently HTC ROM developer @LlabTooFeR posted the roadmap of future Android updates for HTC smartphones. According to the roadmap, the Sense 6 update for the One mini would roll out between June and July.
The Android 4.4.3 update for One M7 and One M8 are confirmed, but these might not be released since these devices could get Android 4.4.4 update directly in July or August. The HTC One M8, One M8 Dual SIM, One Mini 2 and HTC One E8 are expected to get the Android 4.4.4 update between August and September. The One M7 would get this update in July or August.
Android L update is planned for later this year for a range of HTC devices, but the update is under evaluation since the system requirements have not been revealed. HTC One X, One X+, Butterfly and other old devices would not get further update. Check out the leaked roadmap below.