Chrome OS's Dev and Canary update channels bring the latest features before they hit the stable track, but at the expense of bugs and other issues. Many who use Dev/Canary have probably experienced a mini-heart attack upon seeing a "Final software update" message within the past week, but rest assured — it was just an unfortunate bug that's since been fixed.
As reported by 9to5Google, Chrome OS devices on the Dev and Canary channels have been showing the message above for the past week upon restarts, no doubt spreading panic among owners. Luckily, this was just a bug in the newest Chrome OS versions. Google has been developing a feature to inform owners six months before their device's end-of-life date is reached, and an issue caused the warning to appear on every Chromebook that Google has not yet selected an actual final update for.
Devices on Chrome OS Canary have probably already received the update with the fix, though those on Dev might have to wait a few days.
- Chromium Bugs