Nokia/HMD promised minimum two years of OS update support

HMD has made very clear from the beginning that Nokia Android smartphones will be supported with Monthly security updates and regular Android OS and feature updates, whenever available. They have even shown their commitment by releasing Android 7.1.1 Nougat and March, April and May security updates for Nokia 6 in China, Taiwan, and Hong Kong.

The smartphones will get the Android O update once the new release is available from Google for their OEM partners, the same way HMD Global is committed to the monthly Android security updates

But not only Android O, Nokia 3, 5 and 6 will also get Android O successor that can be termed as Android P, if Google Android naming scheme is to be followed. HMD had announced at MWC 2017 that Nokia Android Phones will get guaranteed OS updates for two years. So, Android O roll-out by end of 2017 and Android P roll-out by end of 2018 is almost given for new Nokia Android smartphones.

So, in case you want to buy an Android smartphone to enjoy pure Android experience with latest Android OS version and features, you can certainly go for Nokia 3, 5 and 6 when they become available in the market. Nokia 3, 5 and 6 offer pure Android experience with latest features like Google Assistant out of the box.