Windows 10 Version 1507, codenamed " Threshold 1 ", is the first release of Windows 10. It carries the build number 10.0.10240; while Microsoft has stated that there was no designated " RTM " build of Windows 10, 10240 has been described as an RTM build by various media outlets. It has been retroactively named "version 1507" by Microsoft per its naming conventions for future stable releases of the operating system. The final release was made available to Windows Insiders on July 15, 2015, followed by a public release on July 29, 2015. As of August 2, 2016, the Threshold 1 release is the only available release in Long Term Servicing Branch .