The new Windows Phone 8.1 update 1 Build 8.10.14203.306 has arrived for developers preview devices and these are some changes that we could notice.
1) Battery Saver tile now is a real-time updated Live Tile showing battery percentage.
2) You can add Battery saver as one the quick action settings
3) You can now schedule the incoming Windows Phone updates
4) 4G option is added as the “Highest connection speed” in India. Don’t know whether this holds for some other regions too.
5) UI navigation is more fluid
6) Network Time protocol works correctly for more
Do let us know, if you can notice any other changes?