Traditionally, Microsoft has developed Windows releases using codenames so that secrecy about product features is kept, and unofficial information doesn't get leaked. Each release of Windows 10 also has its own code name. The initial release was internally named 'Threshold', which was followed by 'Threshold 2'. Five releases after it were codenamed 'Redstone'. This has changed.
For reference, here are the previous codenames for Windows 10 releases:
- Threshold 1: Windows 10/1507
- Threshold 2: Windows 10 November Update/1511
- Redstone 1: Windows 10 Anniversary Update/1607
- Redstone 2: Windows 10 Creators Update/1703
- Redstone 3: Windows 10 Fall Creators Update/1709
- Redstone 4: Windows 10 April 2018 Update/1803
- Redstone 5: Windows 10 October 2018 Update/1809
- 19H1: Windows 10 April 2019 Update/1903
As you may already know, the upcoming version of Windows 10 which is due for release in the first half of the next year has the '19H1' codename. This version will probably be made available publicly in April 2019. Now information has leaked that the version that will be released after 19H1 is codenamed 'Vanadium'. For those of you who are not aware, Vanadium is a chemical element with atomic number 23. The release following that is rumored to be codenamed Vibranium.
So it looks like Microsoft is going to use real and fictitious names of elements from the periodic table as Windows codenames. That's probably because Windows engineering has moved into the Azure group, which uses the same naming scheme.
So, instead of '19H2' which everyone expected to see as the codename for Windows 10 version 1909, it will be internally called 'Vanadium'. Don't be surprised to see Windows 10 Codenamed 'Chromium' some day.
For those who are curious about past codenames, here they are for notable releases starting with Windows 3.1.
- Windows 3.1: Janus
- Windows for Workgroups 3.x family: Sparta, Winball, Snowball
- Windows NT 3.1: NT OS/2
- Windows NT 3.5: Daytona
- Windows 95: Chicago
- Windows 95 OSR2: Detroit
- Windows NT 4.0: Shell Update Release
- Windows 98: Memphis
- Windows 2000: No codename
- Windows Me: Millennium
- Windows XP: Whistler
- Windows XP Service Pack 2: Springboard
- Windows Vista: Longhorn
- Windows 7: Blackcomb, Vienna
- Windows 8: Metro/Jupiter
- Windows 8.1: Blue