The OnePlus 3T, the improved, Qualcomm Snapdragon 821-packing version of the OnePlus 3, came out of the box with Android 6.0.1 (Marshmallow), despite Android 7.0 (Nougat) being widely available at the time of its release in late November. This irked some users, but most decided to buckle down and wait it out, especially with OnePlus' devices' excellent reputation for custom ROM support; if a user wanted Nougat too badly to wait, they could always flash a custom ROM. Still, seeing an update that's not Nougat come through could irk some. This update, however, does bring fixes for a number of day-one issues that OnePlus 3T owners faced, some of which are minor, and some of which were likely pretty frustrating.
For starters, the update fixes the serious lag that users were experiencing when the phone dropped below 5% battery. Throttling devices with low battery is common, but can usually be turned off, for those who want to wring every last drop of performance possible out of their phone, and OnePlus 3T owners now have that option. Along with that, Battery Saving Mode will now set the Orientation and Location settings back to the way they were when it is turned off. The update also brings tweaks to how the phone works on T-Mobile US' LTE network, and some connectivity fixes for Mazda vehicles. If you're a WhatsApp user then you should notice that the flashlight is now usable again within the app which could come in handy, because who knows when you might need a flashlight. The update also includes non-specific stability and bug fixes.
The update may not be Nougat, but it will be a breath of fresh air for many frustrated OnePlus 3T owners laboring under the bugs listed above, or hankering for better performance on low battery or better speeds and coverage on T-Mobile US. The update is set to go out incrementally, with a small chunk of the OnePlus 3T user base seeing the update available today, then the rest of that group seeing the update roll out over the coming days. One user is reporting that they tried to install the update and got a failure notice, then tried again and had it available, so trying twice, perhaps with a reboot in between, could help impatient users to get the update quicker, though this user was not corroborated. The update brings the Oxygen OS version up to 3.5.4.