Microsoft announced yesterday, users who are still running Windows 10 1809 received the 1909 version automatically. Anyone who clicks on Check for updates button will have received the feature update.
So Windows 10 1909 is Automatically Installed on Windows 10 1809. Devices running previous will automatically the get enablement Package of November 2019 update to activate the modifications. The only thing will remain is to restart the system. You can manually get the same KB4517245 to Enable Windows 10 1909 Feature Update.
Windows 10 1909 is Automatically Installed on Windows 10 1809
Microsoft decided that because the end of support for Pro and Home 12.05.2020 is not so much far. So they offered Master switch KB package to enable the features in one turn only.
As you know Windows 10 1909 has workout for the Performance part of the version rather features. And users are getting fewer errors and bugs in comparison with the earlier editions. So the intention to upgrade 1809 automatically would possibly avail them an error free OS version moreover serve a better version.
1] Generic Product keys to Install Windows 10 Version 1909
2] Windows 10 November 2019 Update Installation Blocking issue Fixed by Microsoft
3] Fix: Error 0x80073701 in KB4524570 for Windows 10 1909
4] Administrative Templates for Windows 10 Version 1909 [.admx]
5] Fix: Windows 10 November 2019 Update Bugs and Issues 
6] Windows 10 November 2019 Update Features and Improvements 
7] Windows 10 1909 Changelog
8] Windows 10 Version 1909 ISO [Download]
Source – Microsoft help.