Windows 10 version 18277 is an interim release for development and testing.
The focus assist which first was seen with the Window 10 1803 has en updated to make it more practical. Now when doing anything full screen it can enable focus assist. This will be good for watching movies etc.
The action center now has a slider to adjust the screen brightness. This is very handy for those who are using mobile machines and need to extend battery life.
More Emoji are also being added. This will bringing it to version 12. Still tweaks might come as it has not been finalized yet.
More work with high DPI displays and Win32 applications. Microsoft started working on that with version 17063. Reading glasses can go far to make small things more legible.
WIndows Defender can now manage the camera and microphone more securely. This will allay concerns about privacy.
The Japanese IME is refreshed, this will be popular as media in Japan is still impeded by the way the language is written. Now the candidate is cleaner and more polished. The predictive test is also improved.
Integrating Alexa and Cortana is now being worked on. The Amazon Echo device can now call up Windows 10. via Cortana and vice versa.