Can I use my Windows 7 license key when doing a clean Windows 10 USB installation?

I've now clicked the "Get windows 10" button on the taskbar of my Windows 7 Home Premium installation, and gotten the email confirming I'm eligible for a free Windows 10 upgrade. The instructions says I'll need the License Key if I'm doing a "first time installation":

If you will be installing the operating system for the first time, you will need your Windows product key (xxxxx-xxxxx-xxxxx-xxxxx-xxxxx). For more information about product keys and when they are required, visit the FAQ page.

Even though I proceeded to read the FAQ, it's not perfectly clear to me if the product key on a sticker of my old Windows 7 box can be used on a clean Windows 10 installation, or if I'll receive a new license key some time during the installation. Anyone know this?

I attempted to install Win 10 using a Win 7 Home Premium key I knew to be good - wouldn't work.

What did work was installing Win 7, activating it, and then running the Win 10 installation on it. The installer won't ask for a key at all.

Good luck!