OnePlus One when was launched came with an exclusive custom variant to the phone which is CyanogenMod 11S it was based on Kitkat 4.4 but it was an exclusive customization over the normal CyanogenMod 11 which was denoted by S behind the 11 making it 11S and same went with the Android 5.0 Lollipop variant from Cyanogen the CyanogenMod 12 which was too customized for OnePlus and even Yu Yureka by Micromax.
OnePlus One was known for its customization options that came with Cyanogen's operating system, but the phone was too itself capable to make a hype. Cyanogen made a partnership in India with Micromax which lead OnePlus to develop Oxygen OS for its smartphones, the Oxygen OS was released just earlier this month.
Cyanogen break their deal with OnePlus to move forward with other Chinese brands making them available worldwide. Cyanogen's CEO Kirk McMaster strongly believes that if it weren't for the Cyanogen name, OnePlus would not have enjoyed a successful first year of operations. Executive says,
"Without Cyanogen, OnePlus would have sold like one device in international markets, Essentially they built their brand on the back of Cyanogen."
The statement by Cyanogen doesn't falls good because they literally think that OnePlus is because their operating system, which to our feel is not a correct statement given by Cyanogen. As for OnePlus, the focus is now on producing updates for its OxygenOS. Cyanogen looks like that will provide support for the 12S Android 5.0 operating system, but they will not launch the next build for OnePlus One.