HMD Global’s Chief Product Officer, Juho Sarvikas, has announced that the company has started rolling out the Android 9 Pie update for the Nokia 8 Sirocco. The update apparently started rolling out yesterday, and should hit all units in the coming days.
While HMD is yet to release details about the incoming update, XDA member @peddarson posted a screenshot which suggests that the update comes with a file size of 1379.5MB and carries the build number V4.1.20. It also includes the December Android Security patch.

Screenshot courtesy @peddarson (via XDA)