Writing in a forum post, the smartphone start-up revealed the over-the-air update is due on or before March 30.
It also confirmed that the official release of OnePlus’ custom-built Oxygen OS Lollipop-based ROM will be available to download on or before March 27.
Google first showed off Lollipop back in September last year, and released the source code for the software over three months ago.
OnePlus One users have been patiently waiting for the upgrade ever since, particularly as most major manufacturers have now managed to push the update to flagship devices.
“First, there was an unforeseen OS signing issue, which has recently been resolved. Our camera module had stability issues on Lollipop, and we had to rebuild it for compatibility. Several other crucial drivers, including our Wi-Fi drivers, also needed to be updated to work flawlessly with the upgrade.”
Related: Best Android Smartphones 2015
It continued: “Admittedly, it took a little more time than we had planned, but we only release updates that we are proud of; that means refusing to take shortcuts or deliver sub-par experiences.”
Somewhat amusingly, OnePlus has offered to give away OnePlus One handsets for free if it doesn’t meet both of the deadlines.
“To show you how serious we are about this commitment to our community,
“If we miss either of these deadlines, we will give away five 64GB OnePlus One devices to our fans.”
Google’s Lollipop updates brings with it improved battery life, 64-bit architecture support, lock-screen notifications, and a refined ‘material design’ aesthetic overhaul.