https://wccftech.com/windows-11-will-be-a-free-upgrade-official-health-checker-confirms/

After the release of Windows 10 back in 2015, Microsoft had promised free upgrades for eligible devices for one year. However, that offer was extended and continues to work to this day. Now that the company is ready to move on with the introduction of Windows 11, it was expected that it'll still be a free upgrade.

This has just been confirmed by Microsoft itself and through its health checker that just went live. Microsoft's system health checker verifies if your device meets the requirements to make the Windows 11 upgrade (shared by @_h0x0d_).