Useful info about Windows 10TP Official builds expiration dates and what will happen when a build expires.

The expiration dates for Windows 10 Technical Preview vary by build number. The table below summarizes the expiration dates for each of the builds we’ve released so far. (Dates are subject to change.)

Build number Expiration warnings begin License expiration date Windows will stop booting
9841 4/2/15 4/15/15 4/30/15
9860 4/2/15 4/15/15 4/30/15
9879 4/2/15 4/15/15 4/30/15
9926 9/17/15 10/1/15 10/15/15
10041 9/17/15 10/1/15 10/15/15
10049 9/17/15 10/1/15 10/15/15

Approximately 2 weeks before a build’s license expires, you will start getting warnings that this build will expire and that you should update to the most recent build.

When the build reaches the license expiration date, the system will automatically reboot every three hours.

Approximately 2 weeks after the license expires, the build will no longer boot at all.

If you are still on an older build and are getting expiration warnings, it is likely that Windows Update is failing to install the latest build automatically. To resolve the problem, download the latest ISO file from After the download is complete, double-click the ISO file to mount it and then launch setup.exe.

If Windows has stopped booting due to an expired license, to resolve the issue you’ll need to download the ISO file from another computer and then transfer the ISO file to installation media such as a USB flash drive or DVD. Then boot the PC from the installation media to install the latest build of Tech Preview.

I don't know if this source/table will be updated on new builds arrival, I sure hope.