The Development Codename (“20H2”)
Each Windows 10 Update starts with a development codename. In recent years, Microsoft has simplified these.
For example, Windows 10 20H2 became the October 2020 Update. It was named “20H2” because it was planned for release in the second half of 2020. Simple!
In theory, these development codenames are just that: For the Windows development process and Windows Insiders. In practice, Microsoft has a lot of documentation that uses them, referring to “20H2” and “20H1.” These modern development codenames are easy to understand, and it’s clear that a lot of Microsoft employees prefer them.
These development codenames appear to be replacing the version numbers in Windows 10’s interface. If you head to Settings > System > About, you’ll see the development codename presented as the “version” under Windows Specifications.
Here’s a list of Windows 10’s development codenames for updates, in order from most recent to oldest:
20H2 became the October 2020 Update. 20H1 became the May 2020 Update. 19H2 became the November 2019 Update. 19H1 became the May 2019 Update. Redstone 5 became the October 2018 Update. Redstone 4 became the April 2018 Update. Redstone 3 became the Fall Creators Update. Redstone 2 became the Creators Update. Redstone 1 became the Anniversary Update. Threshold 2 became the first November Update. Threshold 1 became the original version of Windows 10.
Windows 10 receives two of these updates a year. In 2019, you can see that Microsoft shifted to a simple naming system denoting the year and a half of the year the update was released in.
Prior to that, Microsoft named these updates “Redstone,” after a type of block in Minecraft, which Microsoft purchased. Threshold was the original codename for Windows 10.
The Marketing Name (“October 2020 Update”)
But normal people don’t understand development codenames, right? To make things “simpler” for the masses, Microsoft created official names for each update, designed to make them nice and human-readable. When an update is near release, it gets one of these names.
In recent years, these names have been pretty self-explanatory. “October 2020 Update” and “May 2019 Update” are easy terms to understand. That’s the month and year the update was released. It’s more precise than “20H2” and “19H1.”
These names generally appear in blog posts and slick marketing videos and not in the Windows 10 operating system itself.
We call them “marketing names” because that’s what they clearly originally were. After an uninspired first update name (the “November Update”), the marketing team kicked into action. A year after release, Windows received the “Anniversary Update”—a pretty good name, really.
Things then started to become more confusing, with Windows 10 receiving a “Creators Update” full of splashy features like Paint 3D and Windows Mixed Reality. That was followed by the “Fall Creators Update” for some reason.
The Fall Creators Update was clearly the low-water mark for Windows marketing names, and Microsoft stopped trying to create flashy names after that.
Despite Microsoft presenting names like “October 2020 Update” as the official ones, many Microsoft documents use terms like “20H2” or “version 2009” instead.
Even Windows 10 itself doesn’t use this name—perhaps because it’s created by the engineers and not the marketing department. As we mentioned above, the Settings > System > About window uses the term “20H2” and doesn’t mention the words “October 2020 Update” at all in seemingly silent protest against these names.
The Version Number (“Version 2009”)
Windows 10 has version numbers which are different from the development codename! It’s true.
The Windows 10 October 2020 Update is technically Windows 10 version 2009. The first two digits represent the year and the last two digits represent the month. Thus, the number refers to… September 2020.
But this is the October 2020 Update, right? Well, yes. Microsoft is confusing once again here, and the version number seems to refer to the month the update was “finalized” (and perhaps released to Insiders,) while the marketing name refers to the update the month was released.
Here’s a list of version numbers for Windows 10 updates:
The October 2020 Update is version 2009, which refers to September 2020 The May 2020 Update is version 2004, which refers to April 2020. The November 2019 Update is version 1909, which refers to September 2019. The May 2019 Update is version 1903, which refers to March 2019. The October 2018 Update is version 1809, which refers to September 2018. The April 2018 Update is version 1803, which refers to March 2018. The Fall Creators Update is version 1709, which refers to September 2017. (It was released in October 2017. ) The Creators Update is version 1703, which refers to March 2017. (It was released in April 2017. ) The Anniversary Update is version 1607, which refers to July 2016. (It was released in August 2016. ) The November update is version 1511, which refers to November 2015. (This one is accurate!) The original release of Windows 10 is version 1507, which refers to July 2015. (Microsoft gave it this version number retroactively, as it was released that month. )
Microsoft is getting away from these numbers, with development names like “20H2” now shown in the Settings > System > About screen and in the winver dialog. (Press Windows+R, type ” winver ” and press Enter to launch it.) In older versions of Windows 10, these screens showed the version number instead.
While Microsoft is downplaying this number, you will see it sometimes. For example, Microsoft’s Windows 10 Update Assistant refers to the October 2020 Update as “version 2009.”
A variety of Microsoft support documents use version numbers like “version 2009,” too.
The OS Build Number (“Build 19042”)
Windows 10 also has operating system (OS) build numbers. During the Windows development process, each “build” of Windows 10 released to Windows Insiders has its own build number.
After much testing and bug-fixing, Microsoft settles on a final build that will be the stable version of the update. When the stable update is released, it still has this OS build number.
The October 2020 Update has the OS build number “19042.” Technically, the full build number is “10.0.19042,” to indicate that it’s a Windows 10 build. Only the last five digits change.
Also, there are minor build numbers—the stable version of 20H2 is initially “19042.572”, but the “572” number will increase as Microsoft issues minor patches for the update.
20H2 is build number 19042. 20H1 is build number 19041. 19H2 is build number 18363. 19H1 is build number 18362. Redstone 5 is build number 17763. Redstone 4 is build number 17134. Redstone 3 is build number 16299. Redstone 2 is build number 15063. Redstone 1 is build number 14393. Threshold 2 is build number 10586. Threshold 1 is build number 10240.
These numbers tell us something interesting: 20H2 looks like a minor update to 20H1, and 19H2 looks like a minor update to 19H1. This is true—both 20H2 and 19H2 were minor updates with few changes over the previous release.
The numbers in between are development versions of Windows 10 that are sometimes released in preview form to Windows Insiders. For example, build 19023 was an early version of 20H1 released to Insiders during the development process. There was no build 19024 released publicly, but there was a build 19025, suggesting that build 19024 was a build kept internal at Microsoft and never released.
Various Microsoft documents refer to Windows build numbers. For example, a document on a feature might say it was added in a specific build, so you can see exactly when it appeared in the Windows development process. If you search for information about a specific build on Microsoft’s Windows Insider blog, you can see what final update version a build correspond to—for example, that build 19023 document says it’s an early build of 20H1.
So What Do You Do With All This Information?
At times, it seems like different teams at Microsoft are speaking different languages. One document talks about 20H2, another talks about version 2009, a technical document refers to build 19042, and the marketing team talks up the October 2020 Update. They’re all talking about the same thing.
Now that you understand this, it’s easier to make sense of the mess of version numbers you see across Microsoft’s websites and within Windows 10 itself.
We recommend using Google or another web search engine as a translation tool. If you see a document talking about “version 1903,” “build 18363,” “19H2,” or the “Fall Creators Update” and you’re not sure what it’s talking about, perform a web search for that term and you’ll find the other names corresponding to that update.
Hopefully, Microsoft will simplify things further. The confusing year+month version numbers that don’t actually correspond to the month the update was released are being downplayed, which is a good start.
