This is how you can check the version of Chrome OS that your Chromebook is running

Selecting Additional details will provide you with more information on Chrome OS’s inner workings. Select Change channel, for example, if you want to know which channel your Chromebook is on — in other words, the operating system setting. Stable (the default, secure version of the OS), Beta (which gets new features about a month before Stable), and Developer (unstable) are the options (which lets you try out features that are still being tested).