We all know the day is going to come, but as in life, for most chromebook models, we don't quite know for sure when it will be.
It's a little complicated.
A quick glance at the footnotes on Google's Chromebook End of Life policy will give you a gist of the policy -- for the vast majority of chromebooks, Google only guarantees Chrome OS updates for five years from the date of the model's introduction into the marketplace.
There is however, still a chance you may get security or even full updates after that. The dates listed on Google's Chromebook End of Life Policy are just minimum projections, or in other words the earliest the hardware will be rendered obsolete. Devices that are definitively obsolete are annotated when they reach the end of their life.
Even after the EOL date, there's hope!
Google is currently working with OEMs (manufacturers) to guarantee security updates even though full Chrome OS updates may be beyond the life of the hardware.
In addition to Google's policy page itself, PC World has a much more in depth read on this matter.
Feel free to ask us any questions you may have directly, or in the comments below and we will do our best to find an official answer for you!