slmgr /xpr
Unlike older versions of Windows, Windows 10 uses a persistent activation mechanism. Once activated, your device’s hardware hash is stored on Microsoft’s servers. If you reinstall Windows 10 on the same PC, the activation service can automatically restore your license without needing to re-enter a product key. Windows 10 Activation Service
When you install Windows 10, the activation service performs a "handshake" with Microsoft's servers. slmgr /xpr Unlike older versions of Windows, Windows
From that moment on, the service "remembers" your PC. If you wipe your hard drive and reinstall Windows, you don't need a key anymore. The service recognizes your hardware fingerprint and activates automatically. The Twist: Hardware Changes Windows 10 Activation Service