Windows 10 is an operating system developed by Microsoft. Microsoft described Windows 10 as an "operating system as a service" that would receive ongoing updates to its features and functionality, augmented with the ability for enterprise environments to receive non-critical updates at a slower pace, or use long-term support milestones that will only receive critical updates, such as security patches, over their five-year lifespan of mainstream support. Terry Myerson, executive vice president of Microsoft's Windows and Devices Group, said that the goal of this model was to reduce fragmentation across the Windows platform.^[1]

Windows 10 Insider Preview builds are delivered to Insiders in three different rings.^[3] Insiders in the fast ring receive updates prior to those in the slow ring, but might experience more bugs and other issues.^[4][5] Insiders in the release preview ring do not receive updates until the version is almost available to the public, but are comparatively more stable.^[6]

Mainstream builds of Windows 10 are labeled "YYMM", with YY representing the two-digit year and MM representing the month of planned release (for example, version 1507 refers to builds which initially released in July 2015).

The original version of Windows 10 (codenamed "Threshold 1" and retroactively named version 1507) was released in July 2015. It carries the build number 10.0.10240; while Microsoft has stated that there was no designated release to manufacturing (RTM) build of Windows 10, build 10240 was described as an RTM build by various media outlets.^{[7][8][9][10][11][12]} It was retroactively named "version 1507" by Microsoft per its naming conventions for future stable releases of the operating system.^[13]

Notable changes in this version include:^[14][15]

The final release was made available to Windows Insiders on July 15, 2015, followed by a public release on July 29, 2015. Support of version 1507 ended on May 9, 2017 for devices in the Current Branch and Current Branch for Business; however, devices configured to receive updates from the Current Branch and Current Branch for Business continued to receive updates until June 27, 2018.^[16][17]

The Windows 10 November Update (also known as version 1511 and codenamed "Threshold 2") is the first major update to Windows 10 and the second version of the operating system. It carries the build number 10.0.10586.

New features in this version of Windows 10 include:^[172]

The first preview was released on August 18, 2015. The final release was made available to Windows Insiders on November 3, 2015, followed by a public release on November 12, 2015. Unlike the initial release of Windows, this branch was also made available to existing Windows Phone 8.1 devices and the Xbox One and as a preview release to Windows Server 2016, and was pre-installed on new Windows 10 Mobile devices. Support of this version for users of the Current Branch (CB) and Current Branch for Business (CBB) ended on October 10, 2017.^[173] The last public update was released on April 10, 2018, for Enterprise and Education versions only. ^[16]

The Windows 10 Anniversary Update (also known as version 1607 and codenamed "Redstone 1")^{[243][244][245][246]} is the second major update to Windows 10 and the first in a series of updates under the Redstone codenames.^{[246][247][248]} It carries the build number 10.0.14393. The first preview was released on December 16, 2015. The final release was made available to Windows Insiders on July 18, 2016, followed by a public release on August 2.^{[249][250][251]} This release of Windows 10 is supported for users of the Current Branch (CB), Current Branch for Business (CBB) and Long-Term Support Branch (LTSB).

The Windows 10 Creators Update^[362] (also known as version 1703 and codenamed "Redstone 2") is the third major update to Windows 10 and the second in a series of updates under the Redstone codenames.^[363] It carries the build number 10.0.15063. The first preview was released to Insiders on August 11, 2016. The final release was made available to Windows Insiders on March 20, 2017, followed by a public release on April 5 via Update Assistant, and began to roll out on April 11.^[364]

The Windows 10 Fall Creators Update^[459] (also known as version 1709 and codenamed "Redstone 3") is the fourth major update to Windows 10 and the third in a series of updates under the Redstone codenames. It carries the build number 10.0.16299. The first preview was released to Insiders on April 7, 2017. The final release was made available to Windows Insiders on September 26, 2017 before being released to the public on October 17.^[460]

The Windows 10 April 2018 Update^[536][537] (also known as version 1803^[538] and codenamed "Redstone 4") is the fifth major update to Windows 10 and the fourth in a series of updates under the Redstone codenames. It carries the build number 10.0.17134. The first preview was released to Insiders on August 31, 2017. The final release was made available to Windows Insiders on April 16, 2018, followed by a public release on April 30, and began to roll out on May 8.^[539][540]

The Windows 10 October 2018 Update^[606] (also known as version 1809^[538] and codenamed "Redstone 5") is the sixth major update to Windows 10 and the fifth in a series of updates under the Redstone codenames. It carries the build number 10.0.17763. The first preview was released to Insiders on February 14, 2018. The update was originally made available to public consumers on October 2, 2018,^[607][608] but its rollout was halted on October 6, 2018, due to a serious bug that deletes users' personal files after updating.^{[609][610][611]} On October 9, 2018, Microsoft re-released the update to Insiders, stating that all known issues in the update (including file deletion bug) had been identified and fixed.^[612][613] On October 25, 2018, Microsoft confirmed the existence of another bug which overwrites files without any confirmation, when extracting from a ZIP file.^[614] The ZIP bug was fixed for Insiders on October 30, 2018,^[615] and the public rollout of the update resumed on November 13, 2018.^[616][617]

The Windows 10 May 2019 Update^[690] (also known as version 1903^[691] and codenamed "19H1"^[638]) is the seventh major update to Windows 10 and the first to use a more descriptive codename (including the year and the order released) instead of the "Redstone"^[692] or "Threshold" codename. It carries the build number 10.0.18362. The first preview was released to Insiders who opted in to the exclusive Skip Ahead ring on July 25, 2018. The update began rolling out on May 21, 2019.^[693] Notable changes in the May 2019 Update include:^[694][695]

Windows 10 version 1909,^[749] codenamed "19H2", is the eighth major update to Windows 10 and the second to use a more descriptive codename.^[754] The update is intended to be delivered as cumulative update to the May 2019 Update. The first preview was released to Insiders who opted in to the slow ring on July 1, 2019.^[755]

The next feature release of Windows 10, codenamed "20H1", is the ninth major update to Windows 10 and the third to use a more descriptive codename. The first preview was released to Insiders who opted in to the exclusive Skip Ahead ring on February 14, 2019.^[754]