Update 1: 2019/01/12 1:58am PST
The Nokia 5.1 Plus' source code has been released as well. You can grab it from the same page below, or directly from this link.
HMD Global releases the kernel source code for its devices as per the terms of the various open source licenses it uses.Read More
[Update: Nokia 5.1 Plus too] HMD releases kernel source code for the Nokia 7.1 and Nokia 6.1 Plus was written by the awesome team at Android Police.