While there was no official announcement, there's reason to believe that the latest 10240 build version of Windows 10 is the RTM version. This means Windows 10 is now mature enough to ship to OEMs - which are rushing to get Windows 10 PCs in retail stores shortly after the July 29th launch date of the new OS.
Microsoft announced a new build of its Windows 10 operating system today, with version 10240 deploying to both the “Fast” and “Slow” Windows Insider rings. It’s been widely reported that this is the RTM (release-to-manufacturing) version of Windows, since it’s dropping after new builds are no longer available from ISO versions and must be installed via Windows Update. Microsoft, however, is shying away from such language, and has repeatedly emphasized that this is just the “next” version of Windows.>/blockquote>
There don't appear to be any major new changes in build 10240. It's believed Microsoft doesn't want to use the term RTM anymore because they see Windows 10 as a continuously improving operating system.