Microsoft is releasing the Xbox One April update today, which has been in testing with Xbox Insiders since September. The reason it was being tested for so long, unlike other monthly updates, is because this is the semi-annual feature update that coincides with Windows 10 20H1.
There are a few new features that you'll find in the update, which comes in at around 850MB, depending on which version you're currently on, of course. There's a new "Surprise Me!" button, which picks a random game from your library based on criteria that you set.
Once again, Microsoft is promising Mixer improvements. You can now see emotes and subscriber badges in the chat, and Microsoft says "your Ember messages also get the flare they deserve", promising special styling. You can also use the menu button on your Xbox One controller to access settings like stream quality.
Finally, there should be a simplified layout for the Guide. The default tab is now the first in the list, rather than being centered. Party, messaging, and invites have all been merged into one tab, and LFG has been moved into People. There are now five tabs in total.
You can update your Xbox now through Settings, or it will do so automatically if you have proper power settings for it. If not, you'll be prompted to update at some point. The build number for the update is 19041.1927.