Google's Gboard Go is aimed at low-RAM devices with Oreo 8.1 installed on them. The keyboard, which Google will presumably be launching onto the Play Store in due time, is set to offer users who have devices with a low amount of RAM and the compatible version of the operating system a keyboard with many of if not all of the same features as the original Gboard app, but with a slimmed down size and less power requirements, which should make it run a whole lot smoother on those phones.
just as a comparison, Gboard weighs in at about 69MB in size, while Gboard Go is close to half of that, sitting at about 38MB in size. That's a decent amount less in terms of the size of the APK file. Since this requires Android 8.1 Oreo to be installed on the device, the keyboard will technically only work with a handful of devices, which includes the Pixel smartphones, and some of the Nexus devices. Since none of these really have a low a mount of RAM, it's likely that Gboard Go isn't really meant for these phones, and will more than likely be meant for Android One devices and other low-tier Android phones which are slated to get the update to Android 8.1 at some point in the future, as these types of devices tend to come with less RAM.
That being said, there's no telling when Google will plan to launch Gboard Go onto the Play Store and if it will be available in all regions where most of its other services are already available. Considering other "Go" versions of apps are available in most regions though there's no reason to think Google won't do the same thing with this app. YouTube Go for example, is available in the U.S. although it does have some incompatibility when it comes to certain devices. When it comes to similarities between this and the standard version of the app, there are some things which aren't available, such as sticker and GIF search and the one-handed mode, which were likely cut to help reduce the size of the app and help it use less RAM when operating, which, is going to be all the time since it's the keyboard you'll be using to interact with any area where you need to type.