The 'Atlas' Chromebook could have a detachable display according to some recently discovered details and wording found over at the Chromium Gerrit. A string of text in that post, essentially the label for it, is listed as mb/google/poppy: Add variant for Atlas. Though this might not mean much to the average consumer, the significance here reportedly comes from the name Atlas, which was the Chromebook that was rumored yesterday to potentially come with a 4K resolution screen, and the word "poppy" which is said to be the baseboard for an upcoming detachable Chromebook with a different codename. If Atlas is being worked on with a poppy baseboard, then there is a chance that it too will be a detachable Chromebook, which could give it an edge as not only would it have the ability to sit in laptop and tablet orientations but it would also be the Chromebook with the best display resolution.
Atlas is also referenced with Poppy alongside Nami, which is the Chromebook mentioned above that is thought to be the other detachable Chromebook. This further suggests that the two are being worked on as detachables, and perhaps them being referenced together displays that the two are different variations of a similar Chromebook, though it is worth noting there is nothing to actually indicate this.
There's not a whole lot to go off of in regards to Atlas other than the display resolution and the detachable feature, so for now there's no way to know the screen size of Atlas or what other types of specs it might have. With a 4K screen it's likely to come with a powerful processor and quite a bit of RAM, though, as it wouldn't make much sense for low-end hardware to be paired with a display at such a high resolution. There are a lot of unknown details about Atlas still, but it appears that it may be a Chromebook that leans towards the higher end of the market.