Yes and no.
The initial free upgrade from retail is a Digital Entitlement licence. This uses hardware fingerprinting to lock to your device and is valid for the lifetime of your device. In many ways it behaves like an OEM licence.
If you change hardware significantly you may run into activation issues. Automated telephone activation will not be successful. You need to tell MS chat support that you have changed your motherboard. MS support will then remote onto your PC and inject a new key. There were some unconfirmed reports of people getting full retail keys in the early days. But more recently these have been OEM keys.
In the Anniversary Update you can now link your Windows 10 licence to your MS Account, this allows you to self fix activation problems after a hardware change. This does however mean that you have to login to Windows using an MS Account from now on rather than using a local account.