Both the HTC One M8 and the E8 are almost the same phone, aside from the cameras and slight other differences. So it seems normal that they would get updates at the same time. Today Sprint has released OTA updates for both devices with many new enhancements.
Both devices now have support for international Wi-Fi calling, so if you’re traveling abroad and make calls to US, Puerto Rico, or the Virgin Islands, there will be no charge. But if you’re calling another country, you’ll still have to pay the roaming rates.
There are also some other enhancements in tow for the GPS, ItsOn (Sprint’s services and billing app), accessibility, and security. The E8 also gets Sprint Zone improvements.
The current build number of the software for the M8 is 3.30.651.2 and the E8’s build number is 1.22.651.1. If you’re not seeing the OTA update on your phone, you can go check manually.